I was called this morning by a friend and who Im now trying to help, he is in Spain and staying in a rented house for the summer. He knows a bit about pools as do I but neither of us are experts. The pool condition is less than perfect as chlorine tabs have been used for years and little water has been replaced so we can assume that the CYA is off the scale and there is no possibility of re-filling the pool because there are water shortages in the area!!!
Background; a week ago the pool was green, since that time the pool has been shocked with granular shock (but probably only to 10ppm!) several times and although the water had cleared it was not crystal clear and the chlorine would not hold. This is a 42000 litre pool.
Last night at 20:30 the pool was shocked with 2kg 91% trichlor, I think this should have given 45ppm.
08:30 it was back to 2ppm.
08:30 shocked again to 22ppm
12:30 it was back down to 6ppm
13:30 down to 5.2. At this point though the water was crystal clear.
17:00 down to 2.7ppm.
17:30 shocked with 20kg of 15% bleach (am I right in assuming this is about 18 litres?) I believe will have raised the FC by 65ppm.
The test kit available is not able to test above 13ppm so have suggested diluting the pool water by 10 parts and X10 the resulting reading, is this sound advice?
18:30 the reading is 72ppm
19:30 the reading is 52ppm
Other than adding another 20kg of bleach Im not really sure what to do, any ideas?