New Pool Owner: Two questions

I've owned my first pool for about six months. Coastal So. CA, Redondo Beach.

In-ground, ~20,000 plaster pool with attached spa.
Hayward DE filter w/plunger backwash valve.
1 HP pump
Suction from spa drain and/or single pool skimmer. Equalization line from skimmer well to main drain.
Hayward pool vac plugs into skimmer.

Liquid chlorine as sanitizer.

I've continuously monitored my water with a K2006. Typical test results:
FC 5
CC 0
CH 925
TA 100
CYA 60
Ph 7.6

I am targeting FC of 5 and Ph of 7.4 to 7.6. CH for tap water around here pushes 300 ppm. Former owner said water was replaced three years ago. Evaporation is pretty high now that warm weather is here.

Question 1: Not much I can do about the CH given the cost of water and water use restrictions in place right now. I do notice a bit of calcium scale on the spa seats. The forum experts say liquid chlorine shouldn't raise Ph. I have air to spa jets off. Bather load is non-existent (occasional spa use only so far). But the Ph bounces to 8.0 every 4 or 5 days. I drop it (I should correct more frequently) with 34 oz of HCl.

So, how low can I push Ph before I risk damaging the plaster or putting copper into the water from the heater core, and why does it keep rising?

Question 2: I am going to drop a solar cover onto the pool this weekend, and I want advice on the best filtration set up. Day-to-day filtration pulls from the pool with just enough from the spa to prevent cavitation, with majority of return to spa. Most days I have the pool vac plugged into the skimmer, otherwise I use a diverter valve at the bottom of the skimmer to pull some from the main drain and let the skimmer clean the surface. What's the best approach with the cover on? I'm leaning toward using the diverter in the skimmer to get circulation down to the main drain, and maybe increase the return to the pool instead of having the spa overflow. And do I want to up the FC as the pool temperature rises above 80 degrees?

Thanks in advance for your advice

Is your spa 'spilling' or 'flowing' into the pool?

Continuous spill-over = continuous aeration => continuous pH rise and loss of carbonate alkalinty. See http://pool9.net/alk-step/

OK. I just had to run some calculations.

1. Adjust your pH down to 6.8. See http://pool9.net/muriatic/

2. Use borax to bring it back up to 7.0 http://pool9.net/borax/ Start with 1/2 box doses.

3. Do NOT use baking soda ('Alkalinity Increaser', sodium hydrogen carbonate, "Balance Pak 100") or washing soda ('PH Up', sodium carbonate, "Balance Pak 200").

4. Continue to aerate your pool.


Once your carbonate alkalinity = 60 ppm, you should be able to soften submerged scale if you keep the pH around 7.0 - 7.2.

With respect to your heater corroding, pH values and salt levels are the 2 factors to watch. If your pH is 7.0 or above, it's fine. Do you have a salt system?

With respect to your heater scaling . . . it's almost certainly already happening. Lowering the pH and carbonate alkalinity will help soften and strip the scale.

Ben, Thanks so much for your reply.

The pool and spa are at the same level, divided by a low tile wall with a spillway. I try to keep the water level about an inch below the spillway and the flow over the wall is low, with no obvious bubbles. I can try to fine tune the mixing valves to reduce the flow. I haven't experimented with sending most of the return directly to the pool. There is a makeup line from the pool return to the spa, and that may be enough. That's probably what I'll do when I get the cover on.

If I understand correctly, you're saying that I need to get the TA down to 60 ppm using the aeration method. I have a blower on the spa, which I never use, and that should do the trick. How long do I wait between acid additions as I creep down to 6.8? Using the acid demand test in the K2006, I have an excellent idea of acid volumes for my pool to make small (.2 to .4) changes in Ph, but I'll follow your standard advice to use multiple doses for this big change. Does the borax act as a Ph buffer?

Thanks again.

John

Not your TA, your CA (carbonate alkalinity). TA = CA + ~10% of borates + ~30% of cyanuric acid. So, maybe 80 ppm TA.

Both borates and CYA buffer pH, but not nearly as effectively at pool pH levels as carbonates.