When to Adjust CYA?

[akenis]

I was lazy with setting up the pool this year. Had a little mustard the other week, didn't have time to work on it and just added a little polyquot before going on a week trip.

Huge mustard growth upon return! Low CYA, Low Borates and Low Salt. Would have been easier to adjust earlier!

Discrepancies between pool store and my TF test kit:

Reading store me
Salt 2200 3400
CYA 33 <20

I've been shocking based on the higher CYA reading.... trying to keep it at 19. Pool looks good, but I dropped from 19 to 12 overnight. That was just day one.

My salt reading was done with high FC levels. Does that through me off? Add salt light was on (manual says somewhere between 3000-4000 it comes on) Zodiac recommends 4000 for the SWG. I went ahead and added 1200 parts.... which could either take me to about 4300 or 4600. Manual says up to 5000, higher is corrosive.

My attempt to measure CYA was also done at high FC level. Any effect? I filled up the tube and could still see the disc, so I was less than 20. Why the discrepancy?

Big question is when to bring CYA back up and how much? I'd like to keep it low (whatever it is) until I'm sure the algae is gone so I don't have to shock to extreme levels. Is that a good plan, or should I start bringing it up now and just buy the extra bleach? Thanks!

 

[Bama Rambler]

You need some CYA in your pool while shocking but not a lot. We recommend not going over 30ppm while shocking.

Don't trust the pool store numbers. Trust your TF-100 unless you have a very good reason not to.

You're doing a good thing by using the higher CYA shock value. Better to be little high than too low.

How often are you testing and adding bleach?

Please post a full set of numbers as soon aas you can. It'll give us a better picture of where you are.

 

[akenis]

Thanks,

Just started yesterday, added a lot of stuff. Probably took FC up to 19 three or four times. Full numbers:

PS TF-100

FC 9.5 10 (PS sample was sample at 11am, mine from 14:00 w/ SWG on max. Was about 14 at sunrise. It's off at night)
TC 9.5 <10.5
pH 7.9 7.8
TA 85 75ish
CH 221 320 (their test is for "Total Hardness"?)
CYA 19 <20 (their test yesterday was 33. Nothing added yet. I did not test again, think I have 2 or three more left)
Salt 4000 5200 (I added 1200 ppm yesterday from their 2200 vs. my 3400. Also went from 30-50 Borates w/ Borax?)
Borate - 50
Temp 80


So I think I'm safe to shock based on 20 CYA. I'll go ahead and bring pH back down to 7.5. I'm thinking about going ahead and adding about 20ppm CYA and then shock based on 40 CYA overnight and see how it holds. Then doing a CYA test later before I top it off. What do you think?

 

[Bama Rambler]

I think you should do the overnight before you add any more CYA. That way if it shows that you need to continue shocking your FC level won't be so high. remember you have to lose less than 1ppm FC and have no more than .5ppm CC since you're testing with the TF-100 to pass the overnight loss test. Test after dark and again the next morning before the sun is up.

 

[akenis]

Had a 1.5 drop over night w/ CC less than .5. Took the night reading a little before sunset, so I'm going to consider myself algae free. Going to let FC get back to normal levels and then turn SWG back on.

I went ahead and added 50ppm CYA, so I should be somewhere between 50-70 CYA. I'll wait a few days and test before I top of the CYA at 80.

Looking forward to Trouble Free rest of summer!

 

[Bama Rambler]

I think you're making a mistake. If you're not 100% sure everything is gone and you stop now and you've added CYA, when it starts back outgrowing the chlorine you're really going to have a job fighting it. Will that be worth stopping before you're 100% sure?

 

[frustratedpoolmom]

I agree - if you lost more than 1ppm you are NOT done shocking the pool.

 

[fuzzy_dba]

Had a 1.5 drop over night w/ CC less than .5. Took the night reading a little before sunset, so I'm going to consider myself algae free.
Looking forward to Trouble Free rest of summer!

Finish shocking the pool now and you'll have a trouble free summer. If you are not completely finished shocking you are going to have a "green episode" during the time that everyone is wanting to swim...

Git it taken care of now!

 

[akenis]

Oops? I kind of thought 1.5 was pretty close, given accuracy and errors, and 1/2 hour of very light sun the night before.

Edit: FC at the end of yesterday (full day of sun and almost zero CYA) was off the scale for the basic FC test. I then added the CYA and turned the SWG back on.

I did add the 50ppm CYA, so I think it will take a couple of days for it to dissolve and get an accurate reading. So I don't really know what to shock to if I where to continue shocking right now?

What would be the signs if I still have growth? This was a mustard color algae. I'm guessing the first sign would be my FC going strait to 0. How bout if I just monitor that the next couple of days and make sure it stays around 4?

 

[Bama Rambler]

It's your pool of course, and you're free to do whatever you choose, but What I'd suggest is to bump back up to shock level for 50ppm CYA, turn the SWCG off and perform another overnight loss test, being sure to test after the sun goes down and before it comes back up the next morning.