Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Problem with pH:
pH is not a stand alone value. It is controlled by the minerals and other things in the water. With your high KH you will not be able to keep the pH lower. It will always bounce back up.
Dilute your source water with reverse osmosis, about 75% RO: 25% tap (or whatever your source is).
Then you will have much lower KH (roughly 4 degrees) and the pH will be much more amenable to peat moss, CO2 or other pH lowering materials. It will highly likely be lower even before you add peat or CO2. Just lowering the KH often will lower the pH.
This has almost nothing to do with the nitrate problem.
Nitrate: look at all the sources, and all the removal techniques. When the NO3 is rising there are more sources than the removal techniques can handle. In simple terms GIGO, (Garbage In= Garbage Out) or NINO: Nitrogen In= Nitrogen Out.
Protein in fish food is digested by fish and microorganisms to become (among other things) ammonia. This is acted on by microorganisms (Nitrogen cycle bacteria) to ultimately become nitrate.
Solution: Feed less.
Fertilizers that contain any form of N (NO3, Ammonia, Urea, other) can get taken in by plants, or acted on by microorganisms, but ultimately this is adding more N to the tank.
Solution: make sure in all the ferts you are dosing there is no N in any form.
Tap water usually contains chloramines, which break down to ammonia and chlorine. The ammonia is acted on by microorganisms to ultimately become NO3.
Solution: Use RO or other water without chloramines.
Decomposing things such as fish poop (started out as fish food) and fallen leaves (started out as fertilizer)
Solution: Remove these things before they can decompose.
Plants sequester the N, but until you prune and remove plant parts from the tank the N is really still in the tank. When the leaves fall and decompose they 'un-sequester' the N and it shows up as ammonia which the microorganisms turn into NO3.
Water changes remove the NO3 laden water and replace it with (hopefully) water with no NO3 (or at least we hope so!)
Water changes with gravel vacs remove the organic matter (fish poop, fallen leaves etc) before they can decompose. This is removing N in the form of proteins and other organic molecules.
To affect the net amount of NO3 you need to attack both sides of the equation:
Add less nitrogen.
Remove more nitrogen.
Plants can remove a lot of N if their other needs are met. Like Zapins mentions, I also have found that fully submerged plants are not great N sinks. A whale of a lot better than non-planted tanks, but still, they have their limits.
I have found that plants in contact with the air are better. Partially this is because I am not adding much carbon to my tanks, so I know my plants are growing slower and therefore using less N. But in the air there is all the carbon they could want. My house plants, roots in the tank, leaves in the air, are thriving, and the tanks are showing such low N that I have to dose it. I did not dose it as long as all I had were submerged plants.