Lurker first post asking for advise / opinions, please!

[bobuikcat]

I've owned our 44K gallon SWG, vinyl liner, sand-filter, in-ground pool for about 17 years and have always been very pleased with it. I've used this site and pool school for help more times than I can count but the last two years I've had problems I just cannot get past so hopefully y'all can help me. Several times the last two years, including right now, I've had algae growth even when my FC level was higher than recommended based on the CYA/FC chart. Two weeks ago I came home from a business trip to a green pool. I figured out that the flow sensor for the SWG had malfunctioned and it was not running. I SLAMMED it using liquid shock (not the first time I've had to do it over the years) and after about 4 days passed all the tests (the FC/CC and OCLT passed after the first day but it took three more days until the water was really clear). I turned the SWG back on but at a lower setting (25% versus the %60 I normally run it at) and checked my FC every day which was at it's lowest 13 with a CYA of 70, so well above the target of 5. My PH was a little high (7.8) but everything else was in range. Starting yesterday I have an algae bloom of some sort covering nearly every surface of the pool liner again. It looks brown settled but more green-yellow when brushed. This is the fourth or fifth time in the last two years this has happened and I can't figure out how to get rid of it. The entire pool gets direct sunlight most of the day so I don't THINK it's mustard algae from what I've read. Should I SLAM it and then take it to Mustard Algae levels for 24 hours after passing SLAM? I replaced the sand in the filter weeks ago and it appears to be doing it's job, I also bought a new Nautilus CC Plus cleaner because my 3 year old Kreepy Krauly (third one I've had) was no longer getting the job done. I can't think of anything else to try!

Current readings (have not started SLAM) with TFT100 Kit:

CC=0
FC=16 (I turned the SWG up a little last night)
Salt = 3000
PH = ~7.6
CYA = 80
TA = 70

I will bring the PH down to 7.2, raise TA as necessary and then start SLAM with Liquid shock later today.

Any advice / opinions would be most welcomed, thanks for all the un-acknowledge help over the years!!

Bob K.

 

[AftonJeeper]

Don't worry about the pH and TA right now. With FC over 10 your pH test isn't valid. TA of 70 for a vinyl pool is fine.

If algae keeps coming back I have to think it is still hiding somewhere in your pool. Pull your pool light and any other items that are in the pool and inspect and soak in a concentrated solution of bleach and water. Check your weir doors as well, saw a thread a couple weeks ago that had algae hiding there.

 

[Jezza]

Welcome to the forum.

Have you checked any hidden areas of your pool- behind light niches, around skimmer boxes etc.

Also are you regularly brushing your pool?

Notwithstanding the above, algae means a SLAM and its persistence could indicate mustard algae.

 

[jturie]

+1 on the weir/skimmer thought. Algae loves to hide there, and surprisingly around and under my basket/tophat. I basically swim around the pool wearing my little scrubber mitt and get in all the nooks and crannies in my skimmer. Rest of the pool is spotless, but not there.

 

[bobuikcat]

Thank you all for the suggestions, I don't brush it regularly except for the steps but I do put the cleaner in every other day at least. I was working under the assumption that the high level of chlorine would kill off the algae even if hidden but it sounds like that may not be the case. I'll pull the ladder and double check the skimmers and weir doors. The light it a fiber optic unit so I don't think I can pull that out, per se, but I'll get in and try to scrub around it thoroughly. Also thanks for the note about the PH and TA tests, I'll just start the SLAM now and then raise it to MA Shock level once it passes the "big 3" just for good measure. Thanks again!

 

[tim5055]

I was working under the assumption that the high level of chlorine would kill off the algae even if hidden but it sounds like that may not be the case.

Some types of algae actually develop a bio-film that protects it from the chlorine, kind of like an armor suit. Brushing breaks up the biofilm and allows the chlorine to work

Additionally, some areas (lights, in ladders) may not have sufficient water flow for the chlorine to get to the algae. If nothing else in these areas the brushing can help get chlorine everywhere.