pump filter not working

[koagirl]

We have a 15,000 gallon above ground pool. The filter is not filtering. We vacuum and it shoots the algae back into the pool. Any suggestions, ideas? We have a sand filter and it's worked fine the last two summers. We replaced the sand last year. Thanks so much!

[PoolDoc]

The most common reasons for the problems you describe are that (a) the algae is still alive OR (b) your filter needs more (not new) sand, because your pump's too big and you lose some each backwash . . . or BOTH (a) & (b).

[koagirl]

thanks, I'm guessing it's B (we've been backwashing every day, sometimes multiple times a day because we've had so much algae) didn't know we lost sand when se did that. I'll tell the hubs and we'll check the sand. I'll read the link immediately. Thanks!

[Watermom]

You should only backwash a sand filter whenever the pressure rises 8-10 psi over the clean filter pressure.

Welcome to the Pool Forum, by the way!

[koagirl]

Thanks pool doc. So if the problem is the sand, how much do we add? How do we now how much to add?

[PoolDoc]

Here are the manuals:
http://www.pentairpool.com/pdfs/sanddollarDS.pdf
http://www.pentairpool.com/pdfs/sandfiltergenericOM.pdf

You can empty it -- be CAREFUL of the laterals!! -- and fill it with 150lbs, or your can add sand till it's within about 6" of the low part of the water inlet on the bottom of the valve. If the existing sand is gummy or in big lumps, replace it.

By the way, you listed your maximum depth as 4' and your shallow depth as 4.5'. Not sure what you mean by that, BUT the maximum volume for a 15' x 30' oval with an average WATER depth of 3.9' is only 7,700 gallons.