So, longer story, it might help to fill in all the evidence. I do self maintenance, sometimes well, sometimes not so good. In the last 3 years the pool has gotten out of control much more often and I can't get it back.
10 years ago I got new equipment installed, a Sta-Rite System:3 filter with 300 sq ft of cartridge filters. The cartridges are now 10 years old. Prior to that I had a DE filter.
With the DE filter, when the pool got out of control, I could treat it all, clean the DE panels, etc. Then as a test I would empty the jacuzzi, return water to the jacuzzi, and it was crystal clear coming back. And so just continued to filter the pool.
Now with the cartridges it doesn't come back clear. In the past 3 years I've drained it, replaced the water at least 3 times -- cheaper than buying hundreds of $ of Leslie's junk they want to sell me.
So my main question is about the filter. Why doesn't it come back clear like with my old DE filter? I've added some DE to the cartridges, thinking that would help, but it doesn't. In the process of all of this, I've cleaned the cartridges about 3-4 times a year, no obvious holes, maybe I need to do a very detailed inspection. I am starting to be against the cartridges based on my good experiences with DE. My research has some people saying to replace the cartridges every 2-3 years, others claim they should last 7-10 years.
So, I need a plan. I see a few different paths:
1. Convert my Sta-Rite System:3 (model S7M120) to DE, parts are about $850-$950, plus some cutting to insert a backflow valve. There is conversion kit available (P/N 25021-1021) but I really don't want to do this work or spend that much. Then educate myself here on the forum about "real" pool care.
2. Buy new cartridges, looks like about $400 - $500 (this is my big hiccup), every 2-3 years? Yikes! and then, self education here on the forum and get it cleaned up.
3. Try to clean it up first (i.e. follow advice here to get proper test kit, reeducate on chemistry, etc.). The either get the new cartridges or convert to DE after it becomes mostly clear. I have no confidence it will clear up. (I can't kill everything, no problem, 3 bottles of bleach from the price club).
4. Just drain / refill again, buy new cartridges and assume everything will be fine without finding the root cause of the problem. (potential $500-$600 expense without any assurance that it will be better). Draining is easy, we are on a hill, a few garden hoses for siphoning and then muck out the rest.)
Bottom line question: if my old DE system would return clear water after cleaning, why don't my current cartridges return clear water even after adding some DE (and I haven't found a hole in the cartridges yet).