Looking for thoughts on water balance

[sonoman]

SLAM'd my pool in late May because of some algae; took FC up to recommended 24, stable overnight, then let it drift back down. Pool looks great.

Pool still looks clear. Kids are gone so not much use this summer. My wife brushed pool today after about three weeks. She said there was a little algae algae on steps and on west side of pool. Not much and nothing in deep water...she said she probably wouldn't have noticed anything if pool was brushed down weekly. I didn't see it and it could have been dirt because the pool had not been brushed down awhile and it gets dusty around here.

SWG pool, 27k gal, plaster/pebble
Tested with TFTest kit, new reagents this year
FC=3.5
CC<0.5 (she said 1 drop, then cleared)
TC=4
pH=8.2 (adding acid when I get to hardware store later. pH constantly creeps up on me)
CH=350
TA=90 (a little high per TFP recommendations for SWG+plaster)
CYA=70 (hopefully we get more rain next winter to dilute it down some more)
Last time I had salt checked, it was 3200

I am scratching my head why she said we have algae. Maybe it is dirt, not sure

Should I run SWG a little higher? Circupool RJ60+, running about 20% duty cycle to maintain FC~4

Also, why do I struggle to keep the pH down? It seems I am constantly adding acid to it

 

[mknauss]

If the CYA result is from today, you are running at the minimum for FC. That is pretty dicey. Your choice, but bumping FC to 6 or 7 ppm would give you some cushion.
Also, pH does have a minor effect on chlorine effectiveness, even with CYA in the water. A high pH and minimum FC is a recipe for algae.

 

[sonoman]

Thanks, Marty.

I'll bump the SWG up to increase FC.

If I have a recipe for algae brewing, should I SLAM it again or watch it for time being?

Also, how would I have known I have recipe for algae brewing? I aim for the bounds listed in TFP and by the Circupool manual (slightly different, but general agreement).

Thanks

 

[mknauss]

Target FC is 5 ppm for 70 CYA.
pH needs to be in the 7’s.
Do a Overnight Chlorine Loss Test tonight. Raise your FC to 8+ ppm for the OCLT.

 

[sonoman]

Hi Marty,
Quick follow-up. I pushed pool CL up to 9ppm with 1/2 gal of liquid chlorine (left over from my well) and increasing my SWG duty cycle. Acid brought pH down to 7.5. Last night turned SWG off and tested...it took 19 drops 871 to clear. This morning used 18-19 drops of 871 to clear, so I assume algae is not eating my chlorine. Am I good to go maintaining SWG CL above 5ppm?

Why does my pH keep needing acid to keep it down? Pool was re-surfaced to pebble-tec about 10 years ago. Is it normal to constantly need acid to keep in balance?

thanks

 

[mknauss]

Great on the good OCLT. Maintain your FC at the 6-7 ppm level.

What is your fill water TA? How much fill water do you use? Typically a rising pH is due to either TA from fill water or lots of aeration from water features. I add acid to my pool every 2-3 days as I add a lot of high TA fill water.

 

[sonoman]

Fill water from my well, cleaned through water softener, calcite filter, and CL injector. I measured pH 7.5 from the hose bibb early this morning. The auto-fill pulls conditioned water from the same bibb.

For TA, measured 110-120 (barely red at 110, red at 120) for TA. This may explain why TA creeps up on me. Pool TA measured 90 over the weekend.

Your 2-3 days for acid is similar to what mine demands, so maybe I was expecting less fluctuation

 

[mknauss]

With your high TA fill water, adding acid is a fact of life.

If you want to add it less often, add borates. You will still use the same total volume of acid, just get away with out adding it for a week or so instead of every few days.