I need help on how to reduce nitrates, I believe, or am I worrying and over thinking this?
I will be draining the pool to remove nitrates which are around 40+ ppm and to do an iron stain removal service, which is normally done every year but I skipped it last year. By using phosphate remover I was able to keep any algae at bay, however if phosphates go above 1000 ppm green algae appears on the suction pool canister which is near the surface. The water and walls are otherwise algae free. I normally maintain 3 ppm of chlorine with my SWG and pump, running 4 hours per day in a 10,000 gallon gunite pool.
Unfortunately my water supply contains 20 ppm of nitrates, and with the near constant trade winds which blow red volcanic dirt and fertilizer from agricultural fields and occasional vog from Kilauea Volcano (not sure if the vog has anything to do with it) the nitrates increase slowly over time. Phosphates from the water supply register around 200 ppm. I think the reason the numbers are high, on delivery, might be due to volcanic soil and some supplies coming from over fertilized sugar cane and pineapple fields in the past with these chemicals percolating through the soil into the aquifers, although this is pure speculation on my part.
I believe I read that it is possible to reduce nitrates by raising the chlorine to twice the level recommended for Yel/MstrdShock. As my CYA is 30 ppm that would be 18.2 x 2, using the Chlorine/CYA chart, or 36.4, is this correct, and if so, how long would it take to get the nitrates close to zero?
I know that the preferred level for CYA at this site is 80, but I also have an orp controller, and prefer to keep it at 30, so please no insisting on 80 ppm. I am happy where I am, and the automatic acid feed helps control the pH, the acid usage is not that high.
The normal numbers I set the pool at are:
Free Cl 3.0
Temp 80 F - 83 F
Any help would be appreciated, thank you.