Clear water- green dust on bottom

[barbaranna]

You guys helped me clear up my pool water but I always have the same problem every year and dont know what to do about it. The water is clear, the chemicals are in balance with chlorine on the higher side of the ok. But every few days when I go out to the pool on the bottom I see green patches, light green. It isnt something that you have to scrub or anything. I can take my broom and push it and it floats away like brown, very light green dust. even on the bottom that doesnt show green if I push the broom on it there is a slight brown like dust that will float into the water. I kept thinking it was dirt from the trees around my pool. On the sides not a lot but there is some is a couple of spots of green that I can brush away and they are gone. Mostly it ;occurs on the ridge where the bottom and the sides come together. I have shoced the pool when I see this and then it only comes back again within a week. I thought about the yellow mustard kind of algae but it doesnt really look yellow. If I used the stuff to clear up the yellow mustard and it wasnt that would it hurt the pool and make it worse?My water is nice and clear now but dont know what floats on the bottom. Can you help?

[chem geek]

Read the Pool School and in particular note that if you use stabilized chlorine (Trichlor or Dichlor) that this increases the Cyanuric Acid (CYA) level over time making the chlorine less effective to the point where algae will grow faster than chlorine can kill it. If you want to use such chlorine sources, then you need to use a supplemental algaecide (e.g. PolyQuat 60 added weekly) or a phosphate remover (including maintenance doses). OR you can use chlorinating liquid or bleach, but need to add that every day or two unless you have a pool cover in which case you can add it twice a week (that's what I do).

Also note the chlorine/CYA table since the standard recommendations of 1-3 ppm FC don't work to prevent algae growth, especially at higher CYA levels.