Phosphate and phosphate export

[frogdog]

Two questions:

Since phosphate levels seem to be an ongoing issue for reefkeepers and most folks have to use special methods for exporting it, why don't the artificial salt mixes contain less of it, so as to add less to the tank with each water change?

Similarly, why don't the mixes contain more Calcium and alkalinity since that's an ongoing battle too?

Thanks!

Here are some salt mix compositions. http://web.archive.org/web/20001215...om/fish2/aqfm/1999/mar/features/1/default.asp

 

[Randy Holmes-Farley]

Salt mixes generally do not really have enough phosphate to be concerned with. The amount that is there is coming as an impurity in other compounds, not something that is intentionally added. It is a cost issue to drive it lower and lower.

But suppose it is 0.05 ppm in a salt mix and you do a 10% change. Even if the tank had 0.000 ppm phosphate to start, it only got boosted to 0.005 ppm. That is much less phosphate than is added every day from foods.

I discuss those issues here:

Aquarium Chemistry: Phosphate And Math: Yes You Need To Understand Both
http://www.advancedaquarist.com/2012/3/chemistry

from it:

omparison of Food Sources of Phosphate to Other Sources
What about other sources of phosphate, like the "crappy" RO/DI water containing 0.05 ppm phosphate? A similar analysis will show it equally unimportant relative to foods.

Let's assume that the aquarist in question adds 1% of the total tank volume each day with RO/DI to replace evaporation. Simple math shows that the 0.05 ppm in the RO/DI becomes 0.0005 ppm added each day to the phosphate concentration in the aquarium. That dilution step is critical, taking a scary number like 0.05 ppm down to an almost meaningless 0.0005 ppm daily addition. Since that 0.0005 ppm is 40-600 times lower than the amount added each day in foods (Table 4), it does not seem worthy of the angst many aquarists put on such measurements. That said, tap water could have as much as 5 ppm phosphate, and that value could then become a dominating source of phosphate and would be quite problematic. Purifying tap water is important for this and many other reasons.

The same sort of calculation applies to analyzing other phosphate issues, such as the GAC in scenario three. The issue of finding "high" phosphate in GAC soaked in fresh water was frequently quoted as a reason to use one or the other brand of GAC, and probably still is. But simple analysis as shown above for the food rinsing puts the lie to this being a big problem.

One needs to consider how much GAC one will really use in the aquarium and how often it is added in order to interpret how important the added phosphate is. A typical recommendation might be 1 cup of GAC per 100 gallons of aquarium water, and to change it in 4-6 weeks. Let's assume we detect 0.5 ppm phosphate when a teaspoon is placed in a cup of water, and we get scared by the dark blue color during the test. Is this reasonable? That 0.5 ppm from a teaspoon in a cup of water translates to 0.015 ppm phosphate when a cup is used in 100 gallons.

That 0.015 ppm may be significant, being a typical target concentration level for reef aquaria and amounting to about half to a twentieth of the amount added daily in foods, but remember, it is used for 4-6 weeks. During those 4-6 weeks before the next replacement, foods add 50-700 times as much phosphate. So while it is not unreasonable to look for another brand of GAC, to blame phosphate or algae issues in the aquarium on its use would stretch credibility because it is a very tiny portion of the total phosphate being added.

 

[tmz]

Cynthia ,
Thanks for the link ;note the article is 14 years old ; some manufacturers have likely changed their formulas, since. It's still a useful look at typical salt mix contents,though.

Some PO4 is not a bad thing. Living things needs phosaphorus. Food and inadequate export in a closed system like an aquarium cause it to build up to harmful levels. Salt's contribution is insignificant .

Regarding allkinity and calcium, there are limits on the amount of calcium and carbonate that will remain in solution . When calcifying organisms demand more than the salt mix provides ,dosing calcium hydroxide, carbonate and calcium chloride or a calcium reactor are often used to manage alk and calcium levles beyond what a slat mix can provide. Once a dosing regimen for a specific tank is established it's not very hard to maintain . Salt mixes do vary in the amounts of alkalinity and calcium they contain; some will have alk at 8 o so dkh ;some as high as 12 or 13 for example.

 

[Psyops]

With the knowledge of the latter two posters, I feel like I shouldn't even post. But here is goes. Generally you don't want to add too high nutrients than your system so you don't stress out your own inhabitants. Generally you add saltwater mix that is relatively close to your own parameters. Hope this helps.

Alex

 

[frogdog]

The food! The food! I didn't realize the food was the primary source, and it's impossible to avoid the phosphate. From your same article, Dr. Randy, "In order to begin to understand phosphate sources in aquaria, let's first look at foods. Contrary to what many suppose, phosphate is not something that can be avoided in a nutritious fish food. Phosphorus is present in many of the biomolecules of life, so every natural tissue that goes into a fish food will have substantial phosphorus in it. Phospholipids make up a substantial part of cell membranes. " Thanks Doc, and I have/am reading all your reef articles.

So this begs the question, does a GFO reactor eventually become necessary in every reef aquarium? How efficient is having some bags of GFO in a sump baffle compared to using a reactor?

It sounds like macroalgae takes up some phosphate, and GAC takes out a little. So are those two things ever enough to keep the phosphate down to reasonable levels?

I was hoping that with a small low calcium load reef aq, <30G, 10% water changes weekly might be sufficient for keeping phosphate down and Ca/alkalinity up, but based on another of your articles, Doc, now I'm thinking that will not be enough. http://reefkeeping.com/issues/2006-09/rhf/index.php#6

tmz, thank you, point taken with the article date. That crossed my mind, but I couldn't quickly find one more recent. Yes, I was really surprised to see the significant differences in relative amounts of ingredients. Something else to think about.

And btw, I'm okay with the math, just have to blow away some cobwebs. If I get desperate, I can ask my son, the physicist, or my Ph.D candidate daughter.

 

[frogdog]

With the knowledge of the latter two posters, I feel like I shouldn't even post. But here is goes. Generally you don't want to add too high nutrients than your system so you don't stress out your own inhabitants. Generally you add saltwater mix that is relatively close to your own parameters. Hope this helps.

Alex

It does help, and don't feel funny about commenting. RC has reef wizards and academics all over this forum. That's why it's the go-to forum. I think the majority of these folks are happy to teach peons like me, and I really try to help others if I think I can. :thumbsup:

 

[Randy Holmes-Farley]

So this begs the question, does a GFO reactor eventually become necessary in every reef aquarium?

Some export method(s). In addition to GFO, I use macroalgae, skimming, GAC (very little effect on phosphate) and organic carbon dosing (vinegar). Limewater (kalkwasser) addition may also be helping.

 

[Relativity]

So this begs the question, does a GFO reactor eventually become necessary in every reef aquarium?

Some export method(s). In addition to GFO, I use macroalgae, skimming, GAC (very little effect on phosphate) and organic carbon dosing (vinegar). Limewater (kalkwasser) addition may also be helping.

How much cheato do you recommend for a 100 gallon tank.
How much do you use Randy?
What is your po4 concentration in your tank Randy?

 

[Randy Holmes-Farley]

I don't keep track of phosphate. Years ago when I last measured it, it was often around 0.03 ppm.

I grow Caulerpa racemosa as it has outcompeted the Chaetomorpha in my tank, so I conclude it is more efficient at nutrient export.

In terms of macroalgae, as much as you can fit is a good rule of thumb. I have the top of a 44 gallon Brute can totally covered in a thick Caulerpa mat, and a little growing in two other cans.

 

[Relativity]

Did you use a regular bulkhead fitting for the tub
Did you need a overflo inside the tub
What kind of lighting did you use
I think Im going to do the same thing
What is the flow going threw the tub
how big are the other two cans

 

[Randy Holmes-Farley]

My sump is 2 x 44 gallon cans connected with a big bulkhead.

Upstream from it are two more 44 gallon cans. Water coming from the main tank enters one at the bottom and exists a bulkhead near the top, flowing then into the bottom of the second one and out a bulkhead near the top and into the first can of the sump.

The third 44 gallon refugium is run by a pump from the first can of the sump, and back again through a bulkhead.

All of the refugia are about 3/4-7/8 full of rock, with macroalgae and such on top and is lit on top.

The refugia each have a fluorescent flood light from Home Depot (don't recall those details).

Flow through them might be 2 gallons per minute. Maybe more. Not huge.

 

[Pife]

Randy why do you use vinegar instead of vodka?

 

[Randy Holmes-Farley]

In my tank, it was less prone to promote cyanobacteria. Some others have found the same, but it may not always be the case, depending on many factors, not the least of which might be which species of cyano are present in the tank.

 

[Pife]

In my tank, it was less prone to promote cyanobacteria. Some others have found the same, but it may not always be the case, depending on many factors, not the least of which might be which species of cyano are present in the tank.

Thank you.

 

[hart24601]

Randy, if you don't test phosphate when do you replace the gfo? I keep my reactor running probably long after the gfo is exhausted, but I only change it when my phosphates creep above 0.03 (hanna ultra low). Seems expensive to swap it out on a regular basis if it's not reached capacity.

 

[frogdog]

I grow Caulerpa racemosa as it has outcompeted the Chaetomorpha in my tank, so I conclude it is more efficient at nutrient export.

I'm surprised you would choose Caulerpa when it has such a reputation for creating problems and going sexual. That doesn't concern you?

 

[tmz]

I feel like I shouldn't even post.

Alex,Please continue to post. We are all "still learning "and exchanging perspectives,experience and ideas as well as scientific information is a good way to do it

 

[frogdog]

I feel like I shouldn't even post.

Alex,Please continue to post. We are all "still learning "and exchanging perspectives,experience and ideas as well as scientific information is a good way to do it

Thanks tmz. Very kindly put.

 

[Nano sapiens]

One phosphate export method more suited to shallow SBs that is often overlooked is the regular removal of detritus. I have maintained undetectable PO4 levels (Salifert) for years using this method, careful/moderate feeding, Kalkwasser additions and 10%/week WCs.

 

[Randy Holmes-Farley]

I'm surprised you would choose Caulerpa when it has such a reputation for creating problems and going sexual. That doesn't concern you?

Nope.

In the 15 years I've kept it, the normal type of Caulerpa racemsa (round grape type) has never done sporulated. A variant (peltata?) that has a flatter appearance has done that it my tank several times and then died back, but it never caused any problem.

It can get entrenched the main tank and be nearly impossible to remove short of biological means. That did happen. I have a rabbitfish now and there is never any in the display. In fact, I bring it up once or twice a week from my refugium to the display to fed the fish.