Green Stuff....algae or filter problem

Ok...it goes like this...i get some green stuff in my pool periodically and it seems that I can vacuum it up but I see it coming back through my returns....
Here are a few questions...

1. It seems that enough chlorine can effectively kill the algae but does killing it necessarily eliminate the green? Maybe just not enough bleach but I have gone completely nuts a few times over doing it.

2. It seems that the only way I have been able to get the green out of my pool has been to periodically vacuum to waste. Last year I thought it might be my sand or the laterals so I opened up the canister, checked the laterals (fine) and reloaded the filter....same problem. Could it be the multiflow valve? Do they go bad?
It just doesnt seem reasonable that the algae can go into the filter and go through all the sand and still come out the return. Could the multiflow not be directing the water to the bottom or could there be a tube column of water through the sand that is allowing the water to flow through a channel in the sand rather than filtering it? Even though I inspected them carefully, could the laterals actually be bad....they seemed fine.

3. Could I have backwashed all the fine grains out of my sand and only have coarse grains in the filter?

Killing the algae does usually eliminate the green, that's why you see water go from green cloudy to blue cloudy when the algae dies.

You might try CarlD and Poconos' trick of adding a handful of DE to your filter to help filter out the finer stuff, it's possible that the algae is just too fine for your filter to catch. If so, the DE should help. When you backwash, are you getting green water out?

Also, are you using sand or zeolite in the filter? The dust from zeolite is greenish in color, and it is fine enough to escape into the pool, especially at first.

Janet

If you post your test numbers we can eliminate some possibilities.
1) FC
2) pH
3) CYA
4) T/A
5) Calcium Hardness