Mustard Algae / High Stabilizer / High FC / trying to use solar cover

[scc_in_TX]

Fairly sure I have mustard algae after Pool Co left filter open / pump off for 2+days. Then it took 2 more weeks for Pool Co / Property Management Co / Home Warranty Pool Co to fix cracked part inside filter allowing water to bypass cartridge. I'm forced to use all three parties with lease, but did recently change spa light myself as I was tired of waiting weeks.

The light brown dust-like substance clings to side of pebble-coated pool but brushes off easily, clouds, and dissipates quickly. Problem was not resolving on its own and pool wasn't shocked to my knowledge, pool co seemed not helpful, so I decided to add 3 lbs of Shock from hardware store. I also bought test strips also, but didn't record pre-shock results. I was reading a lot of posts indicating that a weekly shock was advisable. The chlorine levels seemed high before I started, but so was stablizer.

Yesterday I ordered a Taylor K-2006 test kit, so hopefully I'll have a better feel for the readings when I get it next week.

Its been three days and I have the following readings using test strips:

TH: 500+
TC & FC: off-scale >10
PH: 7.8
TA: ~20?
Stablizer: 150

I diluted 1:1 with RO water and got:

TH: ~250
TC & FC: off-scale >10 but closer
PH: 6.8?
TA: ~0?
Stablizer: ~75

So I turned the autochlorinator to off (I don't know what exactly is in it...). I'm waiting for the TC/FC to go down but based on stabilizer I may be waiting a long time and I'm still finding brown-ish dust on walls every day. Not as bad today as yesterday. I'm brushing walls daily and running pool vac 12+ hrs.

I'd like to get to the point of feeling comfortable using a solar pool cover and heater but want to ensure the algae and high chlorine levels. Family and friends from Newfoundland Canada are coming Nov. - Feb. and will want to swim / sit in spa. We've just moved to Texas.

I'm thinking the pool water need to be diluted (drain/refill) to reduce the stabilizer and the method of chlorination has to change. In the meantime I'm guessing we need to stay out of the pool??

HELP!!

 

[tim5055]

Welcome to TFP!

The autochlorinator will be filled with 3" tricolor tabs. That is why your CYA is so high, for every 10ppm chlorine added to the pool from these tabs it adds 6ppm of CYA. You have to switch to liquid products or the CYA will continue to rise.

Until you get your 2006 and we can get exact accurate CYA and FC levels we really don't know if your chlorine is high or low.

 

[scc_in_TX]

Thank You.
If I assume that CYA is at 150 (the full strength and diluted strip tests roughly agreed), then I should be aiming for a normal target FC level of 18 ppm, min of 11, and a shock level of 60ppm? And I have to get to at least shock level to get a handle on the algae.

I'm not going to make any more changes until I get better results or FC drops, but I'd like to come up with a plan.

What are these levels going to do to a 16mil solar pool cover?? Or more importantly our skin?

The only way to reduce CYA is to drain and fill a significant portion of pool water and stop using it in any form? (I realize now that my shock was adding stabilizer too.)

Based on my guesstimate of 30k gallon volume (40'x20' almost oval 9' deep with 4' shallow end - again all guesstimates), I'd have to dump then fill 20k gallons to get down to 50 CYA. (assuming it was safe to do that...). If I filled while dumping it would take a lot more water than that.

How did you go about reducing CYA?

What's your recommendation?

I'll talk to pool co and see if they'll cease with the chemicals and just test and advise from here on in. I don't mind taking this on myself if owner and pool co will allow it. But I don't want to have to deal with algae / over-chlorination from their neglect.

 

[tim5055]

You are in a tough spot not owning the pool. Most pool services do not recognize the FC/CYA relationship and just follow the industry line "keep FC at 2 - 4 or 3 - 5".

Without running the numbers myself it sounds right. When I took over my pool CYA was 250ish. I was lucky that it was clear and I did not have to SLAM at those levels.

It is safe to swim up to shock/SLAM level so I would not fear damage to the cover at your levels.

With a cement based pool, the only issue in draining is floating the pool out of the ground if you are in a high water table area.