Hi Chris-n-Tim;
You're in Massachusetts . . . so I'm guessing you may have an above-ground?
A very, very common cause of problems like yours is that pools, and especially AG pools, are installed with big pumps and little filters, when what's really need are little pumps and big filters. The result is the big pump blows the sand out of the little filter, after a season or two. Since there's not much sand, and not much resistance, you'll get "strong pressure coming from return", but the water won't be well filtered. You can get by when all's well, but when you have a pool full of tiny dead algae particles, things don't go so well, because the big pump blows the little algae through the small amount of remaining sand in the little filter.
So . . . the way to test if this IS the problem is to add DE powder, like Janet mentioned . . . and then go watch a return. If you see white DE powder blowing back into the pool, that's your clue: your filter needs work. Actually, what probably is needed is to
1. add sand to the filter;
2. install a valve (or maybe, partially close an existing valve) to SLOW flow through the filter;
3. and look into swapping the impeller in your pump for a smaller one, so you can slow flow without wasting electricity.
If missing sand IS your problem, ironically, this can make clarifier and floc fail. Those products can (don't always, though) make little particles like algae clump together. But, if the (technical language alert!) "shear forces" are too high -- and they probably are in a big pump/little filter situation -- the clumps will be broken apart. Once that happens the floc / clarifier / dirt blend is ACTUALLY harder to filter, and now the floc or clarifier that's attached can make it HARDER to filter the stuff out.
Of course, there are other possibilities. But it would be a good idea to do the DE test, answer the questions Janet listed, and if you can, send pictures of your pool, pump, and filter to poolforum@gmail.com so we can see exactly what you've got.
Good luck.
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