I have two separate issues that I'd like to resolve. The first is the issue of the consistent rise in Ph I see, especially when adding chlorine. I use 12% liquid bleach. First, the numbers:
24,000 gallon in-ground plaster pool
TDS: 500 (measured this weekend, pool was refilled about 6 weeks ago for a patch)
Water temperature is about 84 right now (not heated, just in South Florida)
*see notes below.
First question: when I add bleach to shock -- usually about one and a half bucket, i.e. 3.75 gallons of 12.5% bleach -- I notice a very steep rise in Ph, driving it from 7.5 up easily above 8.2 to where I cannot properly measure it anymore. I know that as the chlorine is consumed, the Ph is supposed to drop again, but that's not what I am seeing. I shocked last night -- pump running all night long -- and this morning, FC is down to about 6 but Ph was still above 8.2. I started at 7.5 before I shocked. Why is this? I though that liquid bleach was supposed to be largely Ph neutral (Ph rises at first and then comes back down as chlorine is consumed). On the whole, I end up using quite a bit of Muriatic Acid to correct for this every time I shock and I'm wondering what it means.
Second question: even though I shocked last night with 3.75 gallons of bleach, I noticed significant algae still this morning. I brushed right after I noticed them -- didn't have time last night -- but I'm surprised. In addition, I had significant cloudiness this morning. Should I be shocking even harder? I do still have about 6.0ppm of free chlorine, which should be enough, but apparently is not. Any suggestions?
Notes: The alkalinity and CYA readings are tricky. As for CYA, I've had one store measure it at 100, another at 50, and my own test kit suggests 30. Not sure what to believe. I can say that when I refilled the pool, I added enough stabilizer to bring it to about 60. Alkalinity is similar story: one store has it at 160, another at 130, and I have two test kits which give me 120 and 150 respectively. The 150 reading comes from the more elaborate Leslie's test kit (recommended here) and the other reading from an OTO test kit. In any case, no agreement on either the CYA or Alkalinity. Stores also tested phosphates at about 200, but my understanding is that they should not matter at all with proper shocking and maintenance. I only use Liquid chlorine, no floating pucks: they gave me the worst CYA problem last year, so I'm trying to do without altogether.