Got new test kit...ready to kill algae and want tips

[sdescant]

I have a nice green pool. Approx 10,000 gal concrete(?) pool with a sand filter. With the new TF-100 test kit I get the following:

FC 5
CC 1
TC 6
T/A 300
CH 750
CYA 70
pH 7.8
Temp 75

Do I need to pull down the pH and/or T/A before shocking? If not, I guess I just follow the instructions as noted in the post on getting rid of your swamp, correct?

Steven

 

[TizMe]

I would work on getting your algae under control first. Follow the steps in the pool school section about getting rid of a green swamp. If anyone thinks you should work on your TA and other things as well they will let you know.

If your able to post pics of the battle so we can watch ! It would also be helpful if you could post your pool specs in your signature so we can give better advice with any pool troubles you might have.

Welcome and Good Luck!

 

[chem geek]

Though you can work on the TA later, I would suggest lowering your pH prior to shocking since adding chlorinating liquid or bleach (or Cal-Hypo) for shocking will raise the pH, at least initially. This is especially important in your case because your Calcium Hardness (CH) is also high. In fact, your numbers that you posted result in a saturation index of around +1.0 so I am surprised that you aren't seeing some scaling.

Is your fill water from a well? If so, that could explain the high TA and CH. I suggest you test your fill water to see its TA and CH (might as well test its pH, though no need to test for CYA).

Assuming your numbers are correct, it would take 72 fluid ounces (that's 9 cups) of full-strength Muriatic Acid (31.45% Hydrochloric Acid) to lower the pH to 7.2 which seems reasonable given the amount of shocking you will do. The pH will tend to rise on its own anyway due to the high TA.

At some point you are going to have to do a partial drain/refill to lower the CYA level (unless your pool has a saltwater chlorine generator, SWG) and depending on your fill water, that could lower the TA and CH somewhat as well.

Richard

 

[sdescant]

Ok, one week ago I started the shocking. Please forgive me, I am at work and don't have my notes on exact numbers from my tests. Per myCYA (70) I needed FC of 20 for shock. Per the pool school, I started checking at 30 minutes, then transitioned to 1 hour when the drop wasn't over 20%, then transitioned to three times per day checking. During this week I have raised the FC level after each drop back to shock. Last night before bed my test showed 17 FC and I left it there. This morning there was no drop: FC of 17. This should indicate no more algae, but my pool is still green. It is a few shades lighter than when I started, but it is still green. Any suggestions?

Steven

 

[chem geek]

Is the green a clear green as opposed to a cloudy green? We should have asked you that in the beginning. The green could be copper. Have you ever used a copper-based algaecide or have any sort of ionization system? Since you had a significant chlorine demand, it does sound like you had algae, but maybe that's now dead and you are left with a color from copper in the water.

Since you don't have an FC drop overnight (and you should check your CC level and make sure it's low <= 0.5 ppm) then try let the FC drop during the day (from sunlight) though not below 7 ppm and then add some acid to lower the pH to below 7.5 and see if the green gets lighter. If it does, then you've got copper in the pool. If that's the case, then in the short run lowering your TA so you can keep a lower pH can help; in the long-run, dilution of the water and/or use of a metal sequestrant (if there's one better for copper) would be required.

I also want to repeat what I said about the very high CH and TA in your pool. Did you lower the pH before doing the shocking? Do you see any signs of scaling -- rough surface on plaster, white stains above water line, etc.?

Richard

 

[JasonLion]

I expect that you are seeing the dead algae. It can take the filter up to a week (or occasionally more) to clear up the pool after the algae is all dead. When you kill algae it often turns white, but sometimes it stays green.

You should keep an eye on the filter and backwash/clean it as needed. If that algae is really all dead, the water should visibly improve each day.

 

[sdescant]

The green is a cloudy green. Hopefully the algae is all dead and it is just taking time for the sand filter to clean it all up.

Richard: no, I didn't decrease the pH before shocking. Also, I tested my fill water (water from the Laredo, Texas municipal water source) and the CH was 320. I forget the other readings, that record is at home.

Next I am going to lower the pH and we will see what happens.

Steven

 

[sdescant]

Ok, the pH is lowered to 7.2, and I think it is looking a little less green, but that could just be suggestion. If it is copper that is causing the green, can I test for it? So far I have not had to backwash the filter for over a week. The current pressure is only 3 psi over normal. If it is a filtering issue, since I have a sand filter, is there anything to do for it or add to it to help the filtering?

 

[JasonLion]

If the algae is dead you should see a visible improvement each day, though it might be a small improvement. If the water is staying much the same from day to day then either the algae isn't all dead or there is something wrong with your filter.

The simplest thing to try is to backwash the filter and see if things are any different tomorrow. Sometimes the pressure gauge gives the wrong reading or other things can be wrong that cause it to read low, even when the filter does need backwashing.

You can also do a test to see if the FC level goes down over night. Test the FC level in the evening, after sunset, and again as early as possible the next morning. If the FC level goes down by more than 0.5 overnight you probably still have live algae.