Thanks for your previous help, Wizard, do you mind giving me more guidance on my best course of action now, short of draining the pool?
You may remember that the pool went totally green ie could not see the bottom, within a week of having 7 people using a small 4x8 metre pool, on holiday. I did the usual, shock with about 1.5kg, later added anti-algae, etc., without result, finally flocking it over two days then vacuuming to waste, which left a pool very acceptable, almost shiny.
But, the chemical tests had a different story to tell. The pH was still between 6.2 and 6.8, chlorine non-existent. To raise the pH I added about 3kg sodium carbonate, over two days, to no effect. Adding several more of the large chlorine tablets did not raise the chlorine level. At this point I purchased a test strip kit, which included an alkalinity test. This agreed with the previous pH and chlorine liquid-drop measurement and gave the TA as 40ppm, and stabiliser 100ppm. To raise the TA I added, over three days, 2kg of sodium bicarbonate, which raised the TA to between 80 and 100ppm. None of the other readings were affected.
To compare the readings (all ppm) with tap water, pool, -pH 6.2-6.8/Tap 7.2: -Ch 0-0.5/Tap 0.5: -TA 80/Tap 120: -Stab. 100-150/Tap100. Pool 29c, about 45,000 litres.
Shall I add loads more Sodium Carbonate to try to lift the pH now that the TA is ok? At the moment the pool looks good but feels and smells a bit like a chemical soup!!! I shower immediately afterwards, as well as before of course.
Incidentally, adding about 0.5kg rapid dissolving Chl. granules raises the Chl. to 6 or over within an hour or two but its all gone in the morning. Im mystified, what else is there?