Saturation Levels for dosing

[MrMarth]

Hello!
I'm going to be dosing my system for Calcium (Calcium Chloride), Magnesium (Magnesium Chloride + Magnesium Sulfate 7:1), and Alkalinity (tbd between sodium bicarbonate and sodium carbonate). What are the maximum concentrations for solutions people have had success with? That is, you didn't need to clean your pumps of buildup all the time and didn't have precipitation in the container or similar problems.

I'd like the higher concentration so that I don't have to refill the container as often.

Doing some quick searches I've found the following saturation levels, though they are theoretical and likely much higher than practical applications would allow. All are at 20C, which is lower than tank/room temperature but leaves a little wiggle room.

Calcium Chloride - 75g/100mL

Magnesium Chloride - 55g/100mL

Magnesium Sulfate - 45g/100mL (26g/100mL as heptahydrate, aka epsom salt)

Sodium Bicarbonate - 9.6g/100mL

Sodium Carbonate - 22g/100mL

So, does anyone have any numbers they go by? Thanks for the help!

 

[bertoni]

This article gives the concentrations for a 2-part:

http://reefkeeping.com/issues/2006-02/rhf/index.php

The alkalinity solutions are near saturation, but the calcium solution could be made more concentrated. You can use the magnesium chloride solution and make it more concentrated, as well, although many tanks don't require automated magnesium dosing.

 

[MrMarth]

It may have been relevant to add that this will be for a 3,265 gallon public aquarium reef tank. You'd think with that kind of water volume that levels wouldn't move much, but I get 20-40ppm drops in less than a week (for Calc, Alk, and Mag).

 

[dkeller_nc]

You might have some real dissolution issues with the alkalinity solutions at the concentrations you've quoted. The saturation level and also the dissolution rate for sodium bicarbonate, for example, are quite sensitive to temperature.

This might be relevant especially in Ontario if your solutions are stored in a storage area that's not heated to "office" temperatures in the winter.

But to be honest, I'm somewhat surprised that you're not using a calcium reactor for such a large exhibit. It's a lot cheaper to supply Ca and Alk (as well as trace elements) with a Ca reactor than 2-part.

 

[MrMarth]

I already run a calcium reactor on the system. A Korallin C10002 Calcium Reactor with Eheim Pump. I run into low pH issues when I have the reactor running at a rate to keep up with calcium consumption. I can avoid the pH issues by using dosing. I've been manually dosing every 2-3 days for a couple weeks and my pH and levels are stabilizing. It may just be that I need a second reactor for the effluent of the Ca reactor to manage the pH before it reaches the system.

Another option is a supplemental kalkwasser system, but that's making my life more busy, instead of simplifying things.

I haven't tried the concentrations I listed yet, I wanted a second opinion first. I would be mixing the batches probably every 7-10 days and it would be in heated conditions at all times. We buy our saltwater constituents in bulk and mix our own saltwater. I'll be going through a lot less than the 25,000 gallon batches of saltwater we make every 1-2 weeks.

 

[tmz]

Kalk on a larger system from a still reservoir via timed peristaltic pump is relatively simple in terms of set up and maintenace ,IME ,vis- a'- vis a calcium reactor and or two part dosing.

 

[bertoni]

Hmm, that's a lot of water! You might be able to reduce the pH effect of the reactor by adding a degassing stage, although I don't know how easy that would be. I would use the 2-part solutions for the alkalinity. The calcium solutions can be a lot stronger. You could look at some of the commercial supplements as a guideline, although they usually have better mixing equipment than hobbyists do.

 

[dkeller_nc]

Based on your system, I'd first suggest simply correcting the pH issue. While I wouldn't recommend adding a degassing air stream on just the calcium reactor effluent (which might have the effect of precipitating calcium carbonate as the CO2 is stripped off and the pH rises), it'd be relatively simple to supply the skimmers in the system with outside air. That'd typically be enough to stabilize the entire system's pH at 7.9 - 8.0.

With respect to the concentration of the 2-part, I'd suggest using sodium carbonate at the concentrations that RHF recommends (which is about twice as concentrated as the sodium bicarbonate solution). What Jonathan suggests is a good idea - while RHF set up his 2-part recommendations so that there's equal volumes of Ca and Alk solutions to be added to achieve a balanced ratio, there's no requirement for that to be the case. You could easily set up your dosing pumps to deliver a doubly concentrated calcium chloride solution at one-half the volume measurement of your alk solution.

But the reason I'd recommend fixing the Ca reactor pH issue is the size of your tank. Additions of Ca and Alk 2-part solutions to a tank with a large collection of rapidly-growing corals can skew the natural ionic ratio of chlorides to sulfates pretty quickly. And with modern salt mixes containing a lot of Mg, the corrective effect of mixing mag sulfate and mag chloride and dosing it along with the 2-part mixtures is generally not enough to maintain the chloride/sulfate ratio. In a hobbyist sized tank, changing 10% of the water every week or so is easily enough to keep the chloride/sulfate ratio from becoming really "off", but doing a 10% change every week in a 2500 gallon tank is a much bigger deal (and expensive).

 

[MrMarth]

I actually balance all of the ions for each salt mix. As I dose additional Na, Cl, SO4, etc. I take it out from the next water change makeup (I don't use premixed salt). Soon I am going to start getting occasional triton ICP testing to be even more accurate.

I'm leaning towards a second Ca reactor chamber and letting it run at a higher rate (high enough for Ca demand). If I start to see calcite or calcium carbonate deposition, I can try adding CO2 absorption media. The fractionator (protein skimmer) for the system already draws air from a different room than the exhibit.

 

[zzz111]

I mix my 2-part at 1.5N, or about 159g/L sodium carbonate for alk. your 22g/100mL should work if you have the storage room always heated. my room can go as low as 15C when I'm out of town and I travel a lot, that limits my alk supplement concentration.

I was considering sodium hydroxide to replace sodium carbonate in 2-part dosing, upside is its high solubility, and its positive effect on tank pH in my case, downside is it's potentially dangerous to operators, and even worse i'm not totally sure what it'll do to my dosing system, that became one of the show stoppers, along with not being able to obtain lab grade NaOH from consumer channels, not sure about impurities in food grade or drain openers.

 

[dkeller_nc]

If I start to see calcite or calcium carbonate deposition, I can try adding CO2 absorption media. The fractionator (protein skimmer) for the system already draws air from a different room than the exhibit.

Keep in mind that removing CO2 from the tank water (and thus raising the pH) will work against preventing calcium carbonate precipitation. Not sure it'd be a noticeable difference going from an average of pH 7.9 to 8.1, for example, but thought I'd point that out.

 

[MrMarth]

I meant within the reactor and lines. I've never seen the precipitation in the main tank.

Thanks for the heads up though.

 

[bertoni]

I haven't heard that people have more issues with calcium precipitation at the higher end of the normal scale, not to any significant degree. You could try feeding the output of the calcium reactor into the skimmer. People have been successful with that in the past. The output of the reactor tends to be a very slow stream, although I don't know about your setup. If the output is slow enough, it can be degassed with precipitation issues by making sure it's dilute adequately. Unfortunately, on occasion, the flow rate through the skimmer isn't high enough, and some precipitation occurs in the skimmer, even on the air injection port. Depending on the ease of cleaning, you might want to consider this approach.

 

[Icefire]

Any reason for doing a 100% water change every 1-2 day?
If you really go thru 25000g of water on a 3250g every 1-2 day, why not adjust your saltmix?

 

[MrMarth]

The 25,000 gal salt mix is for the aquarium as a whole and uses filtered city water. I only make 250 gal batches for the 3250 gal coral tank using RODI.

 

[MrMarth]

The whole aquarium has 40+ exhibits and over 1,000,000 gal water volume.

 

[Icefire]

Oh, that's more clear