+ It's very common for filters to fail, in all sorts of ways. When they do, they don't filter out what they should. Dead algae is very, very commonly hard to filter. Here are several things you can do.
  1. All filters filter better at SLOW flow rates than at HIGH rates. If you have a 2 speed pump, running 24 hours per day on LOW is MUCH better than running 12 hours per day on HIGH . . . and cheaper, too.

  2. You can test to see if your filter is 'broken' by adding 1 - 2 cups of DE filter powder to the skimmer. If the powder shoots back into the pool . . . your filter needs repairs. (Maybe, more sand, or a new cartridge, or something else.)

  3. You can add a clarifier. Not all of them work, and we haven't identified any 'recommended' brands yet. But if you ONLY add a single recommended dose, they will not hurt, and may help. Do NOT over do it: an overdose of many flavors of clarifier can make things MUCH WORSE. So, use ONLY the recommended doses and not a bit more!

  4. You can use polyquat, which is the ONLY algaecide we commonly recommend. But, it's ALSO a very good clarifier. If you use it, don't use another clarifier however. We're not sure how polyquat would react with some of the other products.
We've sometimes suggested adding DE to a filter to HELP it filter. This is an much more 'iffy' thing, than using it to TEST your filter. Regular DE use can damage cartridge media. And using DE to filter, turns a regular sand filter into a TINY DE filter -- you'll have to backwash a LOT, if there's much 'goop' in your pool. So, think twice about using DE to 'help' your filter. The one case where it does seem to work well is when you have a SAND filter and HAZY water -- not very dirty, but not quite clear. In this case, the DE can help remove the stuff your sand is not.

There are other options, too. But these are some of the simpler ones.