adding muriatic acid to covered swg pool

[lauralou]

I live in Atlanta and have a 20,000 gal SWG gunite pool that we have just placed the winter safety-cover on (my pool is nestled among dozens of trees). With the SWG, as we all know, the ph climbs and is lowered by adding muriatic acid. How can I add muriatic acid with a cover on? Is the only solution to unhook some of the safety-cover straps so I can peel the cover back far enough to avoid the acid hitting the cover? Then, how would I brush the bottom of the pool to avoid having the acid drop straight to the bottom? Also, what causes the ph to rise - is it the chlorine setting or the simple act of passing through the cell? In other words, as the water gets colder and the demands on the cell are reduced, does the ph stop rising?

[Sumo1]

Welcome to the Forum! I live in your area and have a similar pool, including lots of trees, but I don't have a safety cover. Once the main leaf drop has finished, I leave the pool uncovered. When the temp gets to 55, I turn off the SWG and just run the pumps 2 hrs each day to work the pool cleaner. That said, if you adjust the pH a couple days before turning off your SWG for the winter, it should be good for quite a while. I might check the balance again in January to see if any adjustments are needed. I think peeling back a bit of the cover is your only application method that I know of.

As for actually adding the acid, pour it in over a return in the deep end, preferably one that is pointed a bit toward the main drain. Make sure the pumps are running as you pour it in and put the main drain on heavy suction to reduce the chances that any of it will pool at the bottom. In this scenario I don't think there's much chance of that happening, especially if you're only adding a cup or two to 20,000 gallons.

By the way, my boys and I swam yesterday! I've had a solar cover on it for the last three weeks and, boy, did it make a difference!! The water was nice and warm...for the first 4-5 inches. Then it was.......BRISK!

Have fun. I hope this helps. I can't help with the 'whys' of SWG pH rise. Maybe Chem Geek will chime in.

Hal

[chem geek]

You are correct that as the water gets colder and the sun is lower in the sky, then the SWG on-time can generally get reduced and this will reduce the rate of pH rise (due to less chlorine and carbon dioxide outgassing). If your TA is high, however, the pH can rise even without an SWG. Lowering the TA level (to around 80 ppm) is one way to reduce the rate of pH rise in general.

[PatL34]

If you have a new pool, or had it relined recently, this could be the cause of the pH rise as well as what Chemgeek mentioned. You will have to keep adding muriatic acid until the pool or lining stops leaching out calcium salts.

Hope this helps.

Pat

[waterbear]

Main reason the pH rises is because of outgassing of CO2. There are several ways to minimize this:

Make sure the CYA level is high enough (usually around 80ppm) minimize cell on time and the generation of hydrogen bubbles that out gas CO2

Keep the TA on the low side (perhaps as low as 60 or 70 ppm) to keep the carbonation level of the pool down so there is less outgassing of CO2

Keep aeration to a minimum. If you have water features that aerate the water such as waterfalls, spillovers, deck jets, or fountains do not run them all the time but only when you are entertaining or using the pool.

Do NOT drop the pH too low. Try not to go below about 7.5-6-7.6 when you lower pH. Remember, the lower the pH the faster the outgassing of CO2.

Keeping a cover on the pool can help minimize CO2 outgassing and keep the pH from rising as fast but remember that the pool does need to be undcovered from time to time so chlorination byproducts can gas off.

Add borates to 50 ppm to introduce a secondary borate buffer. This, along with a TA on the low side as noted above, can help stabilize ph at around 7.7 for long periods of time.