calcium reactor vs dosing

[tmz]

a person would feel beter if there was a calcium controller with probe that would shut it down in case of emergency. i hate these decisions lol

A ph controller can be used to shut it down. The probe can be placed in the tank with a preset point for Ph shutting down the reactor if the ph drops below it. The Co2 addition and ph drop are critical as low ph is related to high CO2. If ph drops to 7.7 in the tank calcium carbonae ( sketal mass, reef rock, sand ,etc) starts t or redissolve.

 

[tmz]

interested in most is the disadvantage and advantage of each method from our experience and not our personal preference which one is better.

I've used all 3 and have stated my preference but I know it may not be the best or preferred course for everyone. So here is a perspective, I hope without bias for each of the main methods:

Calclium reactor( CACO3 reactor):

Dissolves aragonite media via the infusion of CO2 to the reactor chamber creating a low enough ph to dissolve it.
Provides a balanced mix of calcium and alkalinity along with whatever else the specific media being used contains including a bit of magnesium and some impuriites/trace elements.
Equipment needed includes the: reactor,a CO2 bottle, CO2 regulator, riecirculation pump, dosing pump , ph controller.

Two part dosing: calcium chloride and carbonate:

Commercial products which contain some impurities/trace elements and magnesium in the calcium part may be used or the generic recipes using calcium chloride and baking soda/ soda ash may be used.
Calcium and carbonate alkalintiy doses must be delivered in amounts to meet consumption( ie, 20ppm calcium for every 50ppm carbonate alklainty,2.8 dkh) . Commercial products provide balanced dosing guidelines for supplents mixed t oamthc these proportions as does Randy Farley's generic reciepe.
Some extra chloride is added with the calcium chloride part. Chloride is abundant in seawater at 19,000ppm so it's not going to skew it out of balance in relation to sulfate over the long haul . Routine water changes and using some magnesium sulfate when dosing magnesium will keep the chloride /sulfate ratios in line .

Equipment reqired: None, it can be manually dosed; many prefer dosing pumps and timers.

Kalk( calcium chloride ):

This method provides a balanced dose of calcium and carbonate alkainity . It uses CO2 in the water to form carbonate( CO3) as the CO2 joins the oxide
It is self purifying; impurities / trace elments and magnesium precipitate out of the solution due to it's high ph (fully saturated limewater is about 12.4 ph)to form a slurry in the bootom of the dosing reservoir.
Needs to be dosed slowly over a period of time to avoid spiking ph. The amount that can be dosed is limited as no more than 2 tsps will stay in solution in a gallon of fresh water. Generally, dosing no more than 1/4 tsp or 16 ozs of fully saturated limewater in any given hour per 50 gallons of aquarium system water volume will avoid a significant ph spike.
Equipment needed: None ,it can be dosed manually but would require 4 to 5 doses per day to use it for top off without spiking ph. Commonly it is dosed via gravity drips or a perstaltic or diaphram pump and timer from a still reservoir ; sometimes in conjunction with automatic top off equipment. There are also reactors availbe for those who like that approach.


These methods can be used individually or in any combination depending on the needs of the system and the aquarist preference

 

[JAustin]

Well put Tom. With good equipment and a good understanding all three methods are tried and true. The limitation being on the lime water.

To the OP, be sure to research your equipment before you buy it. No matter if it's dosing pumps and timers, or reactors and solenoids.

 

[Puffdragon]

I have used all three. Currently I am using a calcium reactor on my sps heavy tank with kalkwasser top-off and a kalkwasser top off on a softy/LPS tank. All will do what you need if you do your research and set them up correctly. In my experience with a sps heavy larger tank, the kalk will reach a point where two parts will be needed to boost alkalinity and magnesium or evaporation will need to be increased. The tanks I had before were a LPS/softy 40 gallon tank and a heavily loaded sps 120. In the end I was using HCl acid to super saturate the kalk. That has its own dangers, but worked very well since I made sure I had much more lime than needed to get the pH up, then let the water settle.
On my calcium reactor, I have balanced my bubble count / reactor effluent so it will not go below a certain pH. I have a pH probe in the reactor effluent. If you use a calcium reactor, I would clean the pH probe weekly and replace it yearly.

tmz well put, but there is one issue with the kalk description. High pH, above 12 will pull some heavy metals back into solution, so that statement is not entirely correct. This statement is based on the metals precipitation curves used in industrial hydroxide metals water water treatment.

To the OP, test the reactor for leaks and make sure all parts work. I found the second article posted above to be very helpful. Once this is done take your time lowering the pH. I think calcium reactors would be very difficult to run/ adjust in without a good pH meter.

If you want to try another method, it looks like you have some good input.

 

[tmc1313]

As I stated earlier, once I switched to a reactor I couldn't be happier. I have used both methods now and just prefer a reactor. When I was using 2-part I never made up big batches like others, so for me it was kind of a pain. I was dosing via pumps, but made a costly error one time (my fault). My 2-part containers were above my sump and one of my dosing heads popped off and siphoned all of my part B into the tank (good thing I didn't make big batches). This is what it looks like (lesson learned) not pretty:

By tmc13 at 2012-03-06

Anyway, as others have suggested if you go the reactor route, choose a good regulator (I suggest AP regulator), it works flawlessy and I also suggest a pH controller, but not absolutely necessary. Good luck with whatever you choose, you really cant' go wrong either way. This is the set up I went with and am currently using:

By tmc13 at 2012-03-02

 

[ShaunMonahan]

I have a very small 34g sps/clam dominated reef. I use a calcium reactor because I find it very simple to maintain ca/alk.

By manually dosing CaCl, you are adding both calcium and chloride. The calcium ions get taken up by the corals/clam... The chloride ion does not get utilized and continues to build up in your water. Water changes are absolutely necessary to flush the over abundance of chloride ion from your system.

I do not perform a lot of water changes- maybe 5gals every month or so. For me, the ionically balanced calcium reactor is the way to go.

I also find the calcium reactor to be very inexpensive compared to manual dosing. A 10# CO2 tank cost me $20 to fill and lasts me a year+. I use maybe 3-4# of course aragonite/yr which cost a few dollars. With this method, the costs are mostly upfront...

 

[REEF SMAC]

Now I don't have to tweak the cal. reator every few days

I ran a nice calcium reactor setup for a while and things always needing to be tweaked.

I was always fussing with the reactor. The bubble rate would drift, the media would clog, etc.

Just heard to many tweaking stories with calc reactors.

I agree, I've heard way too many of those "tweaking" stories also.
I honestly don't understand the reason for any of these stories.

Those stories come from people who don't understand ca reactors. They are EASY!

Either that or the reactor, regulator, pumps, etc., they were using were junk to begin with maybe? Poor design? Undersized?

I agree they are EASY.

Or I've been extremely lucky? Never had any problems with a CA RX personally.

People have different views on CA CO3 reactors.

That is for sure!

U must know every single person here and individually and personally...

Maybe it would be a foolish statement, if someone actually stated somewhere that they "know every single person here individually and personally."

I'm a doser, never used a calcium reactor. Friends who use calc reactors have to use Phosphate media, due to the production of phosphate from the reactor.


CaptiveReef

Sooo your friends with CA RXs feed their fish?
Your Friends that dose don't feed their fish?

Really?

If you can't use a ca reactor something is wrong with the user not the method. It's a tried and true method.

Again maybe it's the equipment they are trying to use?

Calcium Reactor for nearly 4 years. Rock steady parameters for me. I only have to adjust the output as the coral mass grows. I had to purchase a larger reactor because the corals were out-consuming the output of the first reactor. Both of mine have been Geo. A 618 to start and now a 818.

Sounds like you understand how they work.

Mine has worked out pretty much the same as yours.

What do you think is wrong with the users who find them more difficult and less effective than other systems? Inconsistency, relative complexity of equipment, ph issues , impurities from the dissolving aragonite are all real questions.

That is a great question.

What is right with the users that don't have any of those problems?

I wouldn't say if you can't keep a reef with self purifying ,ph boosting limewater, there is something wrong with you.

Well I guess this would include me because I have been unable to do it for a long time now.

I currently use limewater for 100% of all my top-off through a stirrer and it does not come close to being enough for my system's demand. I would say that my daily evaporation is probably way above average also BTW.

Last time I went to the doctor there wasn't anything wrong with me.

Next time I go see the doctor I'll ask him why my limewater doesn't keep up.

I used my calcium reactor reactor for years . Corals have never been better since I took it off line and put it on the shelf 3.5 years ago..

If limewater alone would cut it, I might do the same. For now it's not an option. I can turn my CA RX down, but not off.

My biggest complaint with limewater is the precipitate crust that grows, plugging the hose where it enters my sump. Constanly builds up there.
Do you have that issue at all?

That and having to refill the stirrer with kalk every 5-6 days. Way more often than I have to refill my CA RX.

Other than that I love it.

For me personally, 2-part with dosing pumps would be my last choice on a larger system.

I was dosing via pumps, but made a costly error one time (my fault). My 2-part containers were above my sump and one of my dosing heads popped off and siphoned all of my part B into the tank

You have to be careful with the dosing pumps. I accidentally changed the mode on my timer and it dumped a full quart of calcium into my tank while I was taking a shower Monday morning. I came down to a snowstorm in my 125. It was crazy! Everything that survived.:lol2:

I know I'm a CA RX fan but doesn't it seem like there a lot more people posting these disaster stories that happened with their dosing pumps, either overdosing or underdosing, or their Kalk overdose, than any CA RX disasters?

Or at least the disasters happen slower with CA RXs?

 

[REEF SMAC]

I thought this was a good article as well-

http://reefkeeping.com/joomla/index...ctors-in-out-and-everything-in-between-part-1

 

[JAustin]

Glad you understand what I was getting at.

 

[tmz]

Either that or the reactor, regulator, pumps, etc., they were using were junk to begin with maybe? Poor design? Undersized?

I agree they are EASY.

Or I've been extremely lucky? Never had any problems with a CA RX personally.


Good it suits you and your goals and you find it easy and reliable.

Nothing is right or wrong with it or other choices.

I, personally do not like the potential for impurities , inconsistency , low ph and the myriad of equipment that needs to be employed and monitored.

It doesn't boil down to the user having something wrong with him or her or having junk equipment. Those characterizations are not respectful of the choices others make and their experiences. They are likely to get push back.

If you are CACO3 reactor fan , talk about your success; with it and details of your method. That's good information for folks to consider and learn from . Saying those who have problems with them are the problem or have junk equipment is not.

I did not intend to comment much on this thread since I don't use a calcium reactor anymore , nor 2 part except for small tweaks, but couldn't let the it works for me if it doesn't for you something is wrong with you comments pass without counterpoint,especially the 2nd time..

It's easy( wont shout it but it's very easy) to dose two part and limewater without the low ph and impurities including phosphate from dissolving aragonite,which is likely a small amount but still there buried in the aragonite crystals along with whatever else is stashed there .

If I were using my CACO3 reactor , I'd do whatever I could to determine which media had the least impurites based on assays if I could find them..

If limewater alone would cut it, I might do the same. For now it's not an option. I can turn my CA RX down, but not off.

My biggest complaint with limewater is the precipitate crust that grows, plugging the hose where it enters my sump. Constanly builds up there.
Do you have that issue at all?

That and having to refill the stirrer with kalk every 5-6 days. Way more often than I have to refill my CA RX. I do not use a stirrer and could avoid refills on my still reservoir (currently once per week) for up to a month if I chose to make it larger. Kalk met all my needs for years; my evaporation is 18 liters on 600gallons,realtively low BTW. .In recent months , in a system stuffed with growing sps I'm up to tweaking with baked baking soda (1 tblspoon and ca chloride ) once per week to maintain 9.3 dkh and calcium 450ppm with a ph of 8.1 to 8.35.

Not real hard to manage a couple of dosing pumps with timers for two part either, I may do that .



I do not have precipitant clogs in the dosing tube . It's several inches over the water in a high flow area in the sump.
When dosing clear limewater above the water that doesn't happen,ime. Frequently stirred limewater that's cloudy still contains extra undissoved kalk which can lead to localized ph spikes at the end of the tube as CO2 from the air reacts or when the kalk hits the sump. If I forget to let the kalk settle after stirring in a new batch, it occurs and a poke with an awl clears it right up. Dosing too much in any given hour can lead to a biotic precipitation as well.

Rather than go into too much detail about limewater here , this current thread has much more detail and examples of several sps tanks running with limewater as the major or sole calcium and alkalinity supplement:

http://www.reefcentral.com/forums/showthread.php?t=2191454

 

[lockrookie]

you guys are making my head spin lol i still havent hooked up the reactor been bus with my twins first birthday. but soon... thank ou al tho for all the information there si so much i still need to learn. not to mention i thinkmylights are under par for the tank i had hoped to upgrade but havent found anything worthy yet

 

[rodneyri]

Ive had my CR going for 4 years now, its been great for me and so easy. Its a DIY reactor with eheim pump, tunze reg. I clean it out yearly and add new media, replace the bottle every 4~5 months i guess and dont do anything else in between.

my bro does dosing, he was using cheap kamoer pumps and about 3 months in the pump stayed on and dumped 5litres of his mix into the tank. He has GHL now and they work good. he mixes every 3 weeks i think.

 

[REEF SMAC]

Either that or the reactor, regulator, pumps, etc., they were using were junk to begin with maybe? Poor design? Undersized?

I agree they are EASY.

Or I've been extremely lucky? Never had any problems with a CA RX personally.


Good it suits you and your goals and you find it easy and reliable.

Nothing is right or wrong with it or other choices.

I totally agree.

I currently use dosing on my QT tank, a CA RX and Kalk on my DT.
They all work just fine IME.

I, personally do not like the potential for impurities ,

This has never been a huge concern of mine. Should it be?
The amount of Phosphate dissolving out of some aragonite seems negligible overall. Just doesn't seem fair to blame my CA RX when I'm dumping in tons of food to feed my overstocked tank full of fish.

In my mind, I'm thinking I could spend a ton more money supplimenting my tank with gallons of 2-Part, just to have a slightly less phosphate addition.
To keep maybe one extra Anthias?

How much phosphate are we really talking here?

inconsistency ,

Not sure what you mean here. The Alk and CA output was inconsistant for some reason?

My Alk and CA has always been very consistant using a CA RX. It rarely changes for months at a time. As the media is used up and my demand, due to coral growth increases, I simply increase the bubble rate slightly and I'm good for several more months. (and/or refill the reactor media)
Turning the bubble rate up and down is all the adjustment I've ever had to do and it's IMO just as easy, if not easier, than adjusting dosing pumps. With a lot more room for error.

low ph

Running my CA RX effluent through a second chamber, my PH being low has never been an issue. A solenoid that shuts of the CO2 connected to a PH probe has worked just fine. Even without kalk it's never gone below 7.9 at night, in the winter, with the windows closed. I can't say 7.9 has ever been a problem. Most of the year it stays between 8.0 and 8.2.
With kalk it stays between 8.1 and 8.4.

and the myriad of equipment that needs to be employed and monitored.

I personally run pretty much the same myriad of equipment with my kalk setup as I do with my CA RX.

I use the same PH probe connected to the same controller to shut off my kalk if my PH get too high (above 8.4).

I use the same Mag Drive pump to supply my DI wate, to my stirrer. This is actually more complicated because this Mag Drive is controlled by a one-shot-relay to add kalk in small doses whenever my PH drops to 8.1.
Instead of just being on 24-7 like the one feeding my CA RX.

Instead of the recirc pump on my CA RX, there is another motor constantly stirring my kalk. I just can't get into stirring mine by hand, nor am I home everyday to do that. I can barely get my wife to add kalk to my stirrer when I'm not home, much less stand there and stir it for me too.

It doesn't boil down to the user having something wrong with him or her or having junk equipment. Those characterizations are not respectful of the choices others make and their experiences. They are likely to get push back.

I never stated that there was anything wrong with anybody.
Nor did I ever intend to somehow imply that.

I was honestly trying to suggest that there are many other reasons why some people may have not had good experiences with CA RXs. Maybe they didn't understand them, as was suggested by someone else, but I think that there are slso many other possibilities, some of which I attempted to list.

I'm sure there are many personal reasons out there. I certainly don't mean to be disrespectful of anyone's choice of what to use.

If you are CACO3 reactor fan , talk about your success; with it and details of your method. That's good information for folks to consider and learn from .

Like I stated before, I have never had any problems using a CA RX.

I built mine myself out of some clear 8" PVC pipe, Eheim 1048 circulating pump, it's upflow, holds about 4 gallons of coarse media, second chamber is made of 3" PVC pipe and holds about 2.5 gallons of media, supplied by a Mag Drive pump, solenoid on the CO2 regulator connected to a PH controller.

I filled it up with media, set the flow rate, set the bubble rate, set the controller to shut off the CO2 if the PH drops below 8.0.

My flow rate stays consistant. I never change it. I clean the growing sealife out the supply tubing at the most every six to eight months.

My bubble rate stays consistant up until my CO2 tank goes empty.
If my CA and Alk levels drift low over time, I will add 2-part to get the numbers where I want them, turn up my CO2 bubble rate slightly to keep them there.
I can go 3-4 months without having to adjust anything.

The inconsistancy of my evaporation rate over the seasons is what effects my CA/Alk levels the most, due to the corresponding change in limewater additions. Not my CA RX.

Saying those who have problems with them are the problem or have junk equipment is not.

Again I never said there is a problem with anyone.

I would say that there are many that have experienced problems with CA RXs and many that have not.

I simply pointed out that there can be many reasons for that. I still think poor equipment could be one of them. I honestly don't know all of the many reasons out there. I would love to know.

For someone to state that they don't use a CA RX anymore because they had to somehow "tweak" it all the time, to me is like someone stating that they tried a skimmer once, couldn't get it to make enough foam, so they just decided to get rid of it and do 100% water changes from now on instead.

There is nothing wrong with someone who wants to do that either BTW.



I've heard and quoted people saying that they have to "tweak" all the time.

I don't know why, because I honestly don't "tweak" mine very often at all.

I've heard and quoted someone who said their bubble rate would drift.

Does their CO2 regulator not work correctly? What causes it to drift?

My bubble rate does not drift.

Someone mentioned their media clogging up.

Is this because it's down flow? Media is too small? Foam pads are too fine?

Personally never had this issue, even going more than a year without cleaning the foam block in the bottom of my reactor.

Some state that their PH is too low.

How low is too low? Is this because their reactor is undersized? Your flow rate is too high? Your bubble rate is too high? Your house is too sealed up?

Mine rarely went below 8.0 at night, even without kalk.

I did not intend to comment much on this thread since I don't use a calcium reactor anymore , nor 2 part except for small tweaks, but couldn't let the it works for me if it doesn't for you something is wrong with you comments pass without counterpoint,especially the 2nd time..

Glad you did comment. Very interesting discussion.

It has worked well for me.
I was interested to know why it didn't work for others.

Again I never said that there is anything wrong with anyone or their choices.

It's easy( wont shout it but it's very easy) to dose two part and limewater without the low ph and impurities including phosphate from dissolving aragonite,which is likely a small amount but still there buried in the aragonite crystals along with whatever else is stashed there .

I agree it is very easy. I use it everyday.

To pick up the slack, I still prefer CA RX over dosing. I'm not convinced the phosphate is enough to worry about and I haven't discovered any pennies in my media yet.

If I were using my CACO3 reactor , I'd do whatever I could to determine which media had the least impurites based on assays if I could find them..

Please do point out some of those essays. I would like to read more info on that myself.

If limewater alone would cut it, I might do the same. For now it's not an option. I can turn my CA RX down, but not off.

My biggest complaint with limewater is the precipitate crust that grows, plugging the hose where it enters my sump. Constanly builds up there.
Do you have that issue at all?

That and having to refill the stirrer with kalk every 5-6 days. Way more often than I have to refill my CA RX. I do not use a stirrer and could avoid refills on my still reservoir (currently once per week) for up to a month if I chose to make it larger. Kalk met all my needs for years; my evaporation is 18 liters on 600gallons,realtively low BTW. .In recent months , in a system stuffed with growing sps I'm up to tweaking with baked baking soda (1 tblspoon and ca chloride ) once per week to maintain 9.3 dkh and calcium 450ppm with a ph of 8.1 to 8.35.

Not real hard to manage a couple of dosing pumps with timers for two part either, I may do that .



I do not have precipitant clogs in the dosing tube . It's several inches over the water in a high flow area in the sump.
When dosing clear limewater above the water that doesn't happen,ime. Frequently stirred limewater that's cloudy still contains extra undissoved kalk which can lead to localized ph spikes at the end of the tube as CO2 from the air reacts or when the kalk hits the sump. If I forget to let the kalk settle after stirring in a new batch, it occurs and a poke with an awl clears it right up. Dosing too much in any given hour can lead to a biotic precipitation as well.

Rather than go into too much detail about limewater here , this current thread has much more detail and examples of several sps tanks running with limewater as the major or sole calcium and alkalinity supplement:

http://www.reefcentral.com/forums/showthread.php?t=2191454

I will check that out thanks.

 

[JAustin]

Originally Posted by tmz
I did not intend to comment much on this thread since I don't use a calcium reactor anymore , nor 2 part except for small tweaks, but couldn't let the it works for me if it doesn't for you something is wrong with you comments pass without counterpoint,especially the 2nd time..

Well here it is a third. If you setup a ca reactor....don't have faulty equipment....and it doesn't work....THERE IS SOMETHING WRONG WITH THE USER.

If you drive your car to work every day and there isn't anything wrong with the car, or other drivers, but for some reason you keep running into things and denting your car....there isn't anything wrong with the car...it's the DRIVER.

I don't know what's not to understand about my statements. I'm NOT calling anybody a moron, stupid, or dumb.

If someone starts a Kalk reactor...forgets to plug it in...and the DHK of their tank drops...not a problem with the equipment, it's the user.

If someone buys two-part containers, dosing pumps, and timers. Gets everything running and can't figure out cal or alk demand and overdoses, it's not a problem with the method, it's the user.

I hope that clears up my statements. I'm not claiming Ca reactors are the best. Perhaps its coming off to you in some kind of tone....I don't know. I like all three methods....and cheesburgers.

 

[REEF SMAC]

Do you prefer to use a cheeseburger doser or a cheeseburger reactor? :lol2:

 

[M007]

PH up, PH down, kalk stirring, pump this, pump that - seriously? My PH, dKH, Ca, and Mg is stable with 3 containers and a good quality doser. I agree CA RX is cheaper to run in terms of media refill but that's about it. I used a reactor for 4 years and it worked well just love the simplicity of dosing, call me simple.

 

[Sps Dream]

those stories come from people who don't understand ca reactors. They are easy!
people have different views on ca co3 reactors. . However, many who choose not to use them or stop using them understand them and alternative methods very well.

+1

 

[chessmanmark]

Such passion about which way is best. Holy cow!

It's nice to know that there are choices out there and that everyone can find one that works best for them.

I do agree that there is a point to be made here regardless of which method you use. If you buy a quality piece of equipment you get better results.

There's too much excitement about this topic so let's use skimmers as an example. If you purchase a cheap skimmer, then you get what you pay for. Now just to be clear, I'm not calling anyone cheap! : )

I have an MRC calcium reactor that I bought second hand, and I have a Deltec reactor that I also bought second hand. Deltec can be pricey you know. I prefer to use the Deltec. Works great and makes my life easier. I used to dose, made my own two part, but I prefer not to mix up chemicals and fill containers.

I was nervous about setting up and using a reactor until I went through the experience. Once I worked through the initial growing pains it was all good.

And all these semantics don't really prove a thing after all. Put your money where your mouth is. Let's see those full tank shots along with your arguments about which way is better. Just to make it interesting.

Here are my dosing pictures

And here are my calcium reactor pictures. I had much quicker growth this time.

 

[tmz]

Well put Tom. With good equipment and a good understanding all three methods are tried and true. The limitation being on the lime water.

To the OP, be sure to research your equipment before you buy it. No matter if it's dosing pumps and timers, or reactors and solenoids.

Thankyou

To be fair both a calcium reactor and limewater dosing are limited by ph effects. Too much low ph calcium ractor effluent at one time will drive ph below 7.7 and skeletal mass will begin to dissolve. Many use limewater to supplement CACO3 reactor output and to balance out some of the ph drop.

 

[tmz]

mz well put, but there is one issue with the kalk description. High pH, above 12 will pull some heavy metals back into solution, so that statement is not entirely correct. This statement is based on the metals precipitation curves used in industrial hydroxide metals water water treatment.

PuffDragon,
That's not exactly right as I read it. I stayed off the finer points on purification for the sake of a readable post. If food grade lime is used and the slurry is not dosed ther should not be any significant impurity in the limewater. It sheds them via high ph and coprecipitation as they bind to other crystals..

In any case ,only a few metals have significant amphoteric solubility, ie solubility increases at low and high ph values. Most hit the bottom of the curve and stay thereabouts.
The notable exceptions in the 12+ph range would be lead, chromium and zinc.
However, the purification involves not only ph related precipitation but co precipitaiton, ie , binding with carbonate and other precipitants.

Here are two links which shed a little more light on this for those inclined toward the more technical aspects. The first includes the solubility curve for most metals and the second by Randy H Farely lays out the processes and elements involved limewater's purifying processes with a special emphasios on the very lethal Cu, free copper. :

http://www.hoffland.net/hydroxide-precipitation.html

http://www.advancedaquarist.com/2003/5/chemistry