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[stevehaigh]

i set up my new concrete pool when i filled it about 3 weeks ago and got the ph to 7.4 using soda ash. i didn't check for a couple of weeks and just checked today and the ph is 8.0

i've started adding acid but wonder what could have caused the big rise in ph? it's rained a bit here, not much but that usually lowers ph anyhow. i havn't had to top up from the well at all.

my best guess is alkali from the concrete walls is somehow getting into the water but i don;t know how that could be because its all tiled with regular pool tile.

any ideas?

thx

[curtklay]

It is not uncommon for a concrete pool to show a high PH when it is new. Keep adding acid and checking the PH daily. Once the acid demand is met, the PH should stabilize. Also keep your eye on the alkalinity as the acid will also lower it. Keep the alkalinity at around 100ppm by adding sodium bicarb (baking soda). This will raise alkalinity without raising PH. When the acid demand is met, PH can be kept at 7.4 and the alkalinity at 100ppm. Check it weekly. Regular maintenance of a concrete pool will require small additions of acid and bicarb, as the PH tends to run high and the alkalinity will lower with the acid additions.

[SantiSuk]

curtklay, on 2012-01-22 12:20:10, said:

It is not uncommon for a concrete pool to show a high PH when it is new. Keep adding acid and checking the PH daily. Once the acid demand is met, the PH should stabilize. Also keep your eye on the alkalinity as the acid will also lower it. Keep the alkalinity at around 100ppm by adding sodium bicarb (baking soda). This will raise alkalinity without raising PH. When the acid demand is met, PH can be kept at 7.4 and the alkalinity at 100ppm. Check it weekly. Regular maintenance of a concrete pool will require small additions of acid and bicarb, as the PH tends to run high and the alkalinity will lower with the acid additions.

I have a newish 70 cu.m. tiled pool, but the return reservoir (quite large at 15 cu.m.) and return channels around the pool are unlined concrete. I suspected that the unlined bits are what are causing the voracious need for acid - about 2 to 3 litres per week for 5 months now. The source well water is almost bang-on ideal in acidity.

Maybe I'll get around to tiling the reservoir and channel but for now its cheaper to keep adding acid.

I have never tested the alkalinity and clearly I should be doing. Where can I get a test kit for total alkalinity in Thailand? I visit Bangkok or Jomtien reasonably regularly.

[stevehaigh]

curtlay, thanks for the detailed reply

i used to have some paper strips that you dip in the pool and they measure about 6 things including TA. i have never seen them here in Phuket, maybe have to buy on ebay (usually better anyhow)

http://www.ebay.com/...=item3f0b14e9dc

i just bought 2 for US $33.78 inc. shipping.  santisuk, if you are interested, you can buy one from me for 1/2 that plus thai post to your house. p.m. me if interested.

i expect it to arrive here in about 10-14days

Edited by stevehaigh, 2012-01-23 12:13:04.

[PoolDoctor]

Yes, alkalinity is the likely culprit.  Alkalinity is a buffer and stabilizer for pH.  Any good pool shop (e.g., Island Pools) in Phuket will have test strips.  We like the AquaCheck strips out of the U.S.

[stevehaigh]

i added about 1/2 liter of HCL to my pool (about 60.000 liters) a few days ago and the ph is spot on now. but i'll check the TA when i get the strips in case there is a hidden problem

[Valentine]

stevehaigh, on 2012-01-24 12:54:38, said:

i added about 1/2 liter of HCL to my pool (about 60.000 liters) a few days ago and the ph is spot on now. but i'll check the TA when i get the strips in case there is a hidden problem

I have found that using saltwater chlorinators the pH tends to be on the hig side. As another poster said keeping the total alkalinity in the range helps stabilise the pH.