TA Spike?

[RonPace]

Please remind me what raises Alkalinity?
I have this on a 108,000l pool. Test from a SCUBA11.

13/06. Previous week warm, high 20s. No rain
TC. 2.1
FC. 1.9
Ph. 7.6
TA. Not measured as I ran out of tablets (but previous week it was 102.
Cy. 57
Added 5 x 255g tabs calcium

21/06. Previous week off the scale - high 30s every day
TC. 0.2
FC. 0.1
Ph. 7.7
TA. 86
Cy. 60
Added 5x255g Tabs calcium plus 3 litres (maybe even 4...) of 'Javel' (bleach at I think 9.2% chlorine)

27/06 (today) Previous week stabilised a bit 30, then back to high 20s BUT, two very heavy rainstorms
TC. 2.5
FC. 2.2
Ph. 7.9
TA. 146
Cy. 65

It is the spike of 146 in the TA today that I question - would heavy rain alone cause this??

[Teapot1]

Your pH has risen a bit so could be that is the variance, if you bring down your pH to the same as before then re test. Adding fresh top up water if that is higher in TA would also do it. My water TA is between 180- 220 so I try to keep hold of the water in my pool as I brought that down to 40 ish

[RonPace]

I was going to ask if a rise of 0.3 of Ph would give such a spike as that on the TA, but I did not note that during the week of high temperatures, I topped the pool up quite a bit.
I have never thought of measuring my tap water! But I have just done so, and I get:

TC. 0.3
FC. 0.2
Ph. 7.3
TA. 202
Cy. 5

So when one tops up a pool, one is raising or lowering the pool by that of the added water. In my case, a good few cms of water at 202...

You say 40-ish. What is a desirable TA of a pool?

What is the TA of rainwater?

[RonPace]

Help clear something up for me whilst on the subject - everywhere there is talk of soda-ash, baking powder, borax etc.
What is the composition of liquid Ph Minus and PH Plus that one buys in the pool shops?

[Teapot1]

For plastic or vinyl pools a TA around 40 or 50ppm gives a very stable pH so anywhere that gives stable pH is fine.
Liquid pH minus is often sulphuric acid, as hydrochloric fumes a bit (doesnt bother me) and hydrochloric is cheaper and easy to buy in supermarkets in france.
Dry pH + you shouldn't need but soda ash wich is sodium carbonate, I have used caustic soda in the past as you need a lot less and its as cheap as chips. Dilute before adding.