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Alkalinity and Phosphates
Intresting subject James. I too have been seeking information but found nutting.
I have high readings of phosphates and am unable to raise Ca higher than 2, which in turn inhibits the raising of GH and KH. No matter how much CaCO3 I add, the reading is steady at 2 as well as GH and KH.
So, I eventually asked a chemist and here is a translation of the answer I got back:
GH, KH och PO4
Since you got high readings of Phosphateions (30-40 ppm), you have even higher values of hydrogenphosphate (HPO4) and dihydrogenphosphateion (H2PO4). Calcium is sedimented solid in the substrate or filter with the phosphateion and hydrogenphosphateion. This is due to the concentration of these ions and the oxygenamount. Concentration of the phosphateion should not be over 1 ppm if you want to avoid this, but this sedimentation starts already at 0,1 ppm. There is a rekommended value for fishes of 0,5 ppm. I suspect that you also add magnesium and it goes the same way as the calcium (also iron). A low oxygen value indicates high load on the substrat. But you'll have to check this yourself.
When you add carbonate (CO3) it's converted to hydrogencarbonate (HCO3) and probably takes it's hydrogen from the dihydrogenphosphateion which is converted to hydrogenhosphateion. What happens then with the hydrogencarbonate since the carbonatehardness doesn't rise? Here I more unsure but there is a couple of possibilities.
1. Plants takes these up.
2. Bacteria/mushrooms that need carbonate in the process of converting organic material, hence the low oxygen. These organisms use hyrdogencarbonate but also carbonatedioxid.
Apart from this I assume you also add other chemicals, so there are uncertenties in this. My advice is to lower the phosphates and solve the calcite (CaCO3) before it's added. You should notice if the biological activety is high thru measuring the oxygen solved in the water.
My reaction to this has been to increase the mikronutrients and the KNO3 until my readings tell me that the tank isn't eating any more than I add. The goal is to have the tank eat up all phosphates without algea returning.
Currently I'm at 60 ml PMDD and 50 ml's of KNO3, added every evening to the 540 Litres tank.
Readings every day is 0,1-0,25 ppm Fe and <5 KNO3 (Hagen testkits). After fighting with this for 15 weeks I now have 5 ppm phosphate and I seem to be unable to get it lower. Probably due to the feeding of frozen foods to the Discus every day.
As for the oxygen; I assume that, since I still have lots of oxygenbubbles hanging on to the Riccia, 6 hours after the lights go out, there is sufficient oxygen present in the tank.
Results: Well, I still have high phosphates (3-5 ppm) and feed mikro and KNO3 like crazy, but the Ca level started to increase when I reached the 5 ppm level of phosphates, which in turn begun to increase GH and KH.
Plants grow good, very good in fact. I have trim stemplants every 2-3 days since they have reached the surface.
I have no algea and even the Rotala Macaranda is thriving.
Phosphates do indeed have a relationship with other chemicals and can not be freely added to the tank without considering the effects.
Phosphates do not induce algeaexplosion on it's own. I conclude that it's okey to add phosphates if you follow this up by also adding plenty of mikronutrients and KNO3 at the same time.
Funny: Instead of trying to limit my tanks for Fe and other stuff (following the theories of algea control), I have gone the other way and supply the tanks with plenty of PMDD and KNO3 due to the high phosphates and get an healthy algea free tank which thrives to the point of trimmings becomming a chore instead of a pleasure :-)
It's an involotary experiment on my behalf, but perhaps there are some daring entusiasts out ther whom are willing to experiment with this and up their phosphates to 10 together with nutrients and report back the results to the list.
If they do get an algea explosion then, why don't I? If they don't, then we have a new way of agea control, right?
Suggestion: If anyone out ther is currently having a severe algea problem to the point of preparing to tear the tank down... Then try this first; Add phosphates and up the levels to above 10 ppm (remember mine was at 30-40 ppm). Increase the amount of PMDD and KNO3 (forget the Mg but increase the K2SO4 as well). Test for NO3 and Fe every evening after the lights go out until you find that the levels are 5-10 NO3 and 0,1-0,25 Fe every evening and continue to add the achieved amounts while maintaining the higher phosphate level.
If my theory is right your algea should be quickly outcompeted by the increased plant growth.
Disclaimer: Providing that you have plenty of light and CO2 already.
> Date: Thu, 2 Jan 2003 21:15:58 -0500
> From: "James Purchase" <jppurchase at rogers_com>
> Subject: Alkalinity and Phosphates
> Cavan asked a question the other day about the possible effect Phosphates
> have on Alkalinity readings. In one form or another, this question has been
> battered around online since at least 1994. I've NEVER seen anyone step up
> to the bat to volunteer an answer. Lots of stuff which says that things like
> Borates, Phosphates and Sulphates CAN add to Alkalinity readings, but
> nothing which says by how much, or to what degree.
> Is there ANY way to separate out the possible interference from Phosphates,
> Borates and/or Sulphates to an Alkalinity reading? The "standard test"
> doesn't seem to be able to distinguish what bases are present, it just
> assumes (and reports) things in terms of CaCO3 (assuming, or at least
> reporting, that all of the Alkalinity is due to OH-HCO3-CO3). Can you take
> the concentration of either Phosphates and/or Sulphates (both of which are
> testable parameters) and, via some mathematical sleight of hand, calculate
> the contribution of these species to Alkalinity?
> I've found some web based reference material from the U.S. Dept. of Energy
> which leads me to believe that it IS possible. They have tables with
> conversion factors designed to be used in boilers when TSP is added to
> increase Alklainity. So _somebody_ has figured this stuff out.
> James Purchase