How much should chlorine level ppm drop?

[smallpooldad]

Firstly to any of you who are able to help thank you.

I am assisting a friend in removing a large amount of black algae from his pool, which he did not wish to drain, we are shocking using 29 ppm chlorine bleach from Wal-Mart.

This arose from very poor maintenance on the part of his pool person 10 CyA, FC 0.5, pH 8.4 and $150 per month!!!! He finally realized that it is better to do it oneself. My feeling is that the pool person deliberately let it go stating that the reason for the black algae was the old delaminating pool and that he knew someone who could re-plaster for less than the going rate! Where I come from this person should be hung, drawn and quartered preferably in reverse order.

If we raise the level to 29 ppm at 6pm by 8am the following morning it drops to about 18 ppm. Does this sound ok or is the drop indicative of algae continuing to eat up the chlorine? Obviously we would like to drop back to normal levels as soon as possible.

We have been at this for 3 days and 98% of the black algae has gone and what remains is very faint. Not sure if we can get completely rid of the remaining algae as it is growing under the sides on some delaminated areas. Please note the pool is 17 – 18 years old and is quite delaminated. He also had the green stuff growing on the walls which has now gone.

The pool looks 98% better, albeit a little cloudy. We are running the pump 14 hours a day and backwashing to clear. He does not like to run it 24/24 so first thing in the morning he manually vacuums the entire pool and backwashes; a little slower method but everyone is happy

Chlorine 29 -18 (will normally be 6)
pH 7.2 (will normally be 7.5)
Alk 85
Calcium 325
CyA 40-45 (Will let it go down to 35)
Salt 3000 (hope to talk him into 3300 – manual states 3000 – 3500)
Borates None (cannot afford it now as he has spent so much on getting chemicals to get it back into shape - in Honululu most chemicals are 1.5 to 2 times more expensive)
20,000 gals Gunite with plaster
Jandy Aquapure 1400 SWG
1 hp Pump
300 lb? Sand Filter
Temp 81 F