It's too easy being green

[jaybee]

I'm a little confused here because I think my 9500 gal above ground pool should be clear but it isn't. Here are my numbers:

Cl--10
pH--7.3
Alkalinity--120
CYA--20

I've vacuumed and backflushed until there's virtually nothing left except little bits of algae that blow right through the sand filter. Cl level has been kept in the 10-20 range continously for the last 4 days. Last night Cl only dropped from 12-10 overnight so it didn't use much. I brushed the bottom before nightfall thinking the Cl would be more effective if the algae is dispersed through the water. This morning I can still barely see the bottom of the ladder. Am I missing something?

[mbar]

You have to keep adding chlorine - but you must be consistant. Don't let it drop down at all. Keep it at 12ppms, and keep the filter running 24/7. If you have a sand filter, you can put a cup of DE in the skimmer. You can also cut the leg off a pantyhose stocking and put it in the skimmer basket - it helps to filter out small particles. I opened my pool to a green swamp on Thursday. Using lots of bleach, keeping my filter running 24/7, and vacuuming everyday with a sock on the skimmer basket, a cup of DE in my sand filter, I now have clear water. It did take 3 full days to get completely clear. Have patience, and keep up with the chlorine. It will clear up.

[duraleigh]

Hi, Jaybee,

If you are seeing visible matter "blowing thru the filter" (i.e. back into the pool thru the return jets) you have a filtration issue.

No filter, sand, de or cartridge, should allow anything visible to reenter the pool. Like Marie said, you have to keep your Cl level up (looks like you're still consuming just a tiny bit) but I think, if I read your statement about visible matter correctly, that your filter is the primary culprit.

It was a good idea to brush up the stuff......but if your filter's at fault, it's a moot point.

[jaybee]

Well, I don't see particles that are visible individually, just a green cloud from the inlet when vacuuming. Does that make a difference?

[duraleigh]

Well, I don't see particles that are visible individually, just a green cloud from the inlet when vacuuming. Does that make a difference?

Absolutely. You should only be returning clear water to your pool. Check that filter. Are you backwashing?

[jaybee]

Yes, we're backwashing. We lost some sand out of the bottom plug during startup, I wonder if my sand level inside the filter is too low. I do have some additional sand and can add that to the filter. I was under the impression that a sand filter is incapable of catching very small algae particles, am in wrong about this?

[aylad]

Your sand filter may not be able to catch as minute particules as a DE filter would, but you still shouldn't have anything visible returning to the pool. Check and make sure you have adequate amounts of sand, and it sounds like you may need to check and make sure that you don't have broken laterals (yes, I know, that means you're going to have to remove the sand that's in there to check). If all checks out, then you might want to take mbar's advice and add a small amount of DE to your skimmer to help catch what's getting through your sand. I have not done this, but a couple of our other moderators have and say it works well. Just make sure you keep an eye on your pressure if you do this.

Keep in mind also that AG filters are frequently undersized for the pumps supplied, and once your algae is dead (yours isn't yet, if it's still green) it may take longer to filter it out of your pool than it would in a pool with a larger filter.

Keep your chlorine level up, keep brushing, and check the sand in your filter.

Janet

[gregugadawg]

Sand filters only filter to about 30 microns, a human hair is smaller than this 30 microns so yeah sometimes stuff will pass through a sand filter such as algae, this is why you need to vacuum to waste when you clean up an algae pool. Or buy a d.e. filter which has one pass filtration and cleans your pool up very fast.

[waterbear]

Sand filters only filter to about 30 microns, a human hair is smaller than this 30 microns so yeah sometimes stuff will pass through a sand filter such as algae, this is why you need to vacuum to waste when you clean up an algae pool. Or buy a d.e. filter which has one pass filtration and cleans your pool up very fast.
It is generally accepted in the industry that a sand filter will filter to about 60 microns, a cartride to about 20 microns and DE to about 6 microns in normal usage. Manufacturers will make claims based on best possible conditions that don't really exist in normal usage. For some perspective on what this means the human eye can detect a particle as small as about 35 microns. A grain of table salt is about 100 microns, talcum power is about 8 microns. A slightly dirty filter will take out smaller particles than a clean one no matter the type of filter (which is why some people add DE to a sand or cartridge) but it also causes the pressure to increase faster (which limits the effectiveness faster with DE and cartridge filters more so than with sand)