What am I doing wrong...I'm lost

[samiguy]

Here's the deal. Very happy using the BBB and TFP. Got the pool perfect! Then, I had an issue with dull looking water, and per instructions, took it back to shock and cleared up as expected. OCLT zero x2 and CC 0. Here's were I have been maintaining the levels:
FC 5-7
CC 0
TA 90
Ph 7.5-7.6
CYA 70
Brushing/Robot at least weekly..low bather load. Looked yesterday and water looked a bit "dull" again. Looked today and found what appeared to be some brown, dead algae/dirt several places. Brushed and it stirred up green. Yep, algae.....geez.
Took the action to bring the Ph down to 7.2 and brought FC up to 16. Brushed pool very well.
So what am I doing or not doing. At these levels, I didn't think that I would be seeing algae again, at least so soon. This really has me confused... Thoughts?????

 

[JasonLion]

While your numbers look good, it doesn't take a whole lot at higher CYA levels for things to go wrong. With CYA at 70, 5 is the minimum FC level you should ever go down to, and it is safer to keep FC at 6+ so you have some margin in case you miss a day or it is extra hot or lots of swimmers one day.

Another possibility is that your CYA reading is actually higher than you think it is. The usual beginner mistake is to read higher than actual numbers, so that doesn't seem all that likely, but it would explain what is going on here.

 

[samiguy]

Pretty sure the CYA reading is accurate. Pulled it up to that level SLOWLY with use of pool-calc and TF100. Thinking about just keeping FC at about 10, but then comes the issue of how to test. Obviously, OTO is out for levels that high and unable to test Ph at those levels, and drop testing gets alot of regent usage. Any other ideas for testing and is my idea of FC at 10 wise? Thanks!!!

 

[JamesW]

For a CYA of 70 ppm, I think that 7 to 10 ppm FC is a good idea. At that CYA level, I will often go to 14 ppm just to be sure that it never went too low.

Just keep plenty of reagent R-0870 and R-0871 on hand and use FAS-DPD to test the chlorine levels. I would suggest two or three bottles of R-0870 and 2 bottles of the R-0871C (2 oz size).

The pH test is OK at 10 ppm, and I have found that it is actually pretty reliable up to 15 ppm FC when the CYA is 70 ppm as long as the test is read right away. Just to be sure, try to measure pH when the FC is equal to or less than 10.

Note that most people can maintain 5 to 7.5 % of the CYA for FC (For a CYA of 70 ppm, the FC would be 3.5 to 5.25) when using a SWG. You might want to run at about 10 to 15 % for a while and then slowly back off until you notice a water quality drop.

You might also want to consider running the pump longer if you use a timer, especially if you have a sand filter.

Another thing to consider is that you might have some mustard algae. I have found that mustard can be very chlorine resistant and that people can pass the OCLT with mustard algae in the pool unless the FC is close to mustard algae shock levels.

If you think that you might have mustard algae, then you might want to go to mustard algae shock level for a while, just to be sure.

When you did the OCLT, was the SWG ON?

 

[samiguy]

For the OCLT, SWG is shut completely off.....