Quote Originally Posted by PMS SAyMI View Post
first problem is although the most of our pools are the typical concrete pools the other common pool here is fibreglass - for some reason unknown to me all fibreglass pools have low ph normal between 6.7 - 6.9, all other chemical values are good but they all have this one thing in common and does not matter how much ph plus you put in they come up for a week and then go back down. - we now just leave them down but your thoughts on this interest me.
Fiberglass pools are common here also. In fact I have one myself and the only reason I know of that the pH would be low is because of the addition of an acidic chemical such as trichlor or dichlor or MPS. Is the TA as high in the fiberglass pools as in the plaster ones? Is acid being added for any reasons? Posting a full set of test results can tell us a lot more about what is going on.

second thing is we have a small portion of pools with a orangey brown staining in the grouting again all chemical levels are fine now my thought is with this it normally starts on the floor and left alone it will rise up the walls you can brush it all off with a normal nylon brush or metal brush but the following week it is back and looking no different, we have tried shocking, tried a anti algae for mustard algae but nothing works. we have even emptied one pool and acid cleaned it but within 18 months it was back - all our pools are brushed weekly and levels are kept within good ranges.
Once again without having water test results it is hard to say what is going on in these pools but I do have an idea. What is the chlorine source you are using? Is it a stabilized chlorine such as trichlor?
Each pool is different, as you well know, and if you can post some of the acutal numbers and puoducts used (chemical names) from your 'problem pools' we might be able to figure out what is going on in them.