I am new to pools after buying a house with an 18K pebbletec gallon pool June 1. We have replaced the pump and upgraded to a SWG shortly after buying it. I learned alot through the process as it was clear the pool guy doing it is not the most academic or exacting type. I've pretty much been on my own with it since June 5th, getting pump timing and chlorine balanced and all. My testing did measure the CYA to be very high, >120, so I did about a 25% water replacement but it still read high it seemed. My targetted FC was around 7. I would add acid every couple weeks. It has looked very good... Until recently:
The water just was not as clear as it once was and was taking on a slightly greener hue (the pool has a large wall of forest behind it so there is always some kind of dark green reflection). By my testing my FC was 6.5 and CC was <.5. I took water into LPS: FC=7.5, TC=7.5, Salt=3500, CH=170, CYA=60, TA=80, pH=8.2, Acid demand=2, Cu=0, Fe=0, Phos=2500 The pool guy there said my chemistries were probably not causing the cloudiness but maybe I was seeing just dirt and pollen and should backwash the filter (I knew it was time to add some more acid, not sure why the phos is up as my pool is above the level of grass).
The next morning, sunday, I downloaded directions to backwash my 48sf DE filter. I did four cycles of backwashing and rinsing. This dropped the water a couple inches. Then starting the pool back up THERE WAS COMPLETE DISGUSTING BLACK/BROWN FLOW FROM THE RETURNS INTO THE POOL. I was hoping this would clear but did not after 30 seconds or so. I shut everything off and cancelled my other plans that morning.
I went ahead and (reading directions) took the filter apart. It looked quite dirty. There was definitely some patches on green algae on the grids in the filter and very dark diatomaceous earth. I took out all the grids and cleaned them. I discovered holes in about half the grid's fiberglass and some cracked plastic ribs. It being Sunday morning I made the decision to try and sew them up with fishing line and plan to replace next time around. It only took a few minutes to sew some good mattress sutures to get the holes closed. I hosed everything off. We were a little pressed for time so I did not soak the grids in acid, I just put it all back together after cleaning.
I filled the water back up, added muriatic acid, and got the filter running. I added the DE back through a skimmer slowly. The returns were no longer black! They were kicking out some DE dust for about 10-15 minutes but then it cleared up. I added about 2 gallons of bleach and put the SWG on superchlorinate setting. I ran the filter and the polaris 380 for two straight days. My filter pressure dropped from 16 pre-clean to 9 after DE added back post-clean.
I did notice that there had been a lot of fine debris/dust/dirt etc settling on the pebbletec that I had been overlooking. The polaris usually runs four hours a day. I took the time to check over the polaris and discovered the tail sweep was not really working right - there were two fine holes in it causing it to not sweep side-to-side. It would just drag behind. I patched these with vinyl patch kit and the polaris zips along now.
After about 36 hours there was dramatic improvement in the pool and at 48 hours it looked very very good. I still had dust to sweep off the steps and get into circulation but the remainder pool floor is 90% better.
Lessons: Backwash the filter on a regular basis, you can at least temporarily patch filter grid holes with heavy fishing line and good knots, and part of what the polaris does is kick that bottom debris up into circulation so the filter can grab it.
What I still don't quite get is why I had apparent algae with FC of 6-7.5 and CC of 0 ??? If my CYA really is >100 like I thought then I could understand but shouldnt I have had some CC measuring? Or was it more related to poor filtration/need to overhaul the filter?
Thanks all! great forum!