RE: In-Ground, DE Filter Pool With Clear Green Water

[barbjack]

We have an in-ground pool that up until recently has had very few problems. This pool is at least 30 years old but has been maintained well the whole time. We re-plastered when we moved in 8 years ago, and it probably will need to be done again next summer.

DE filter, polaris in pool vac with a boost pump. Main filter runs 4.5 hours per day.
Not super sure on the gallons, we think about 35,000 maybe, but it's irregular shaped so it's tough to get a perfect number. I suppose refilling with a meter on the hose would be the best method, can do that when we re-plaster.
About 9' deep, maybe a little more, it used to have a dive board. Auto cover, used most of the time, and a new solar heating system.

Anyway, we've been using the pucks in the floating dispensers, three dispensers and 2-3 puck each depending on the temperature and pool usage. We usually backwash 2-3 times a year, spring, couple times during summer, and sometimes one in fall.

But last year due to some personal stuff, we didn't backwash for about a year. When we back-washed at the start of the summer this year, we realized the DE filter panels needed replacing. Did that and figured we were good to go.
However, slowly we started to get green water and it's been really stubborn to get rid of. We tried upping the pucks but it didn't help, tried some powdered shock about 3 different times, it didn't work. Have not tried liquid chlorine yet.

We test with a small kit that just measures free chlorine, combined chlorine (not sure what that is) and pH. The drops are fresh, but I'm now realizing it's limited. We did find the pH too high,(we thought it was according to the test) at 7.8 and added muratic acid to lower it. It's now kinda too low at 6.8

Just tested now; Free Chlorine 0.6, Combined Chlorine between 1.0 - 0.6
pH 6.8
KH 107.4 ppm

Don't know if KH is important but I had the test kit from an aquarium so though I'd throw it in there.

Seem like it's just too low in Chlorine, but we get this low reading even after refilling all 3 floaters. It's like the chlorine is either not dissolving into the water, or maybe dissipating too quickly. I haven't used liquid chlorine.

I just ordered a new Taylor k600a test kit, so that should help me get a handle on this.

I've also read here that we should be using some kind of stabilizer, pretty sure we haven't used that at least on purpose. It may be in the chlorine pucks but I don't know.

The water is pretty clear, just green. Although since the pH has been low, there's also a slimy film on the water.

Any suggestions or ideas would be really appreciated. Thanks for listening.

Barb