Stubborn algae - Am I getting it yet?

[PoolInMich]

28' x 48" Aboveground, vinyl, sand filter

FC 26
CC 0-0.5 (FC too high for 0.2 increments)
TC 26-26.5
pH 7.8-8.0
TA 200
CH 280
CYA 100
Temp 74-80 (80-85 when using cover)

I have been actively fighting green algae for about a week. Can I get feedback on whether I am beginning to understand the process as well as what my priorities are in addressing different numbers?

Other info: I just got a FAS-DPD kit which produced numbers above. I turned off the automatic feeder and started using 6% bleach. For past couple days I have been using 12% from a pool supply that is priced favorably and am seeing/imagining slight progress. The jet has been turned so there are ripples and it runs 24/7. I have kept solar cover off as warranty dislikes shocking.

Since algae is my main concern, it seems I need to keep my FC at 25 from chart in one of forums and check it several times a day. pH seems high and does not that affect ability of chlorine to work? Is there a target pH for helping with algae? The wheel says my target pH is 7.1, I think, for balanced water.

Using dry acid (test says 4lbs, wary of Muriatic due to asthma and past experience) to lower pH will lower TA some, but not enough according to some guides. Do I want to lower TA (with 20+lbs?!?) by dropping pH low and letting pH rise or should I worry about it after algae resolved.

Is CYA an issue other than it means maintaining FC higher? I will be draining 20-25% for winter and adding new next season which will lower it anyway.

I have seen a lot of information lately but am having trouble sorting it so I get optimal results. It would be nice if there was some sort of flow chart for addressing multiple issues.

I am trying to get it back, or mostly back, to the crystal clear bath water we had in 5 days for a party. Back then FC was at least 5 (test max) and pH 7.0-7.2 with pool covered and 85 temp. I did not do other testing until after problem took hold.

Thank you in advance for your patience and advice.

[debs_pool]

I'm pretty new at this stuff myself -- but I did deal with some mustard algae earlier this summer -- and with the help of this forum -- got rid of the darn stuff.

Are your chlorine numbers staying that high each time you check it? I cannot answer about the pH, but according to the knowledge I've gotten through the forum regarding treatment of algae -- BLEACH BLEACH BLEACH

Keep it at shock levels while checking it (3X a day if possible). I also left my pump running 24/7 while dealing with this (but I always keep it running 24/7)

Have you checked some of the other algae threads (some have pictures -- which helps (did me) you realize you will see the end of the algae!) You might want to check those out.

Hopefully, if you shock the heck out of it, it should be okay in a few days! Sounds like you're on the right track though.

[chem geek]

I wouldn't worry so much about the high TA until your algae problem is resolved. And yes, the high TA makes it harder to maintain a lower pH, but if you can you can just keep adding acid to bring the pH down a bit though that is not your top priority. The higher pH does make the chlorine less effective, but not by as much as you might think (more on that below). A bigger concern is how high your CYA is. When you say it is 100, is it really 100 or is it more than 100 (most test kits only start measuring at 100 -- if the black dot disappears before you get to the 100 line, then you have CYA more than 100 and will have to dilute the CYA cloudy test sample with clear tap or distilled water and then double whatever you measure).

Does your chlorine level hold overnight or is it getting reduced a lot from night to next morning? If it gets reduced a lot, then the chlorine is killing the algae and you have to just stick with it -- at least a drop in chlorine levels overnight would show you are making progress even if it isn't visible yet. Keep brushing the sides of your pool, run the pump and filter 24/7 and scoop up any dead algae each day/night. Even though Ben's chart says 25 ppm of chlorine will do the trick, it may be that you will need even higher levels of chlorine, possibly 40 ppm or even higher, due to the high CYA level you have (even if higher levels of chlorine weren't necessary, it will make the process go faster). It might be easier and more economical for you to simply drain and refill substantial portions (half) of your pool water to get the CYA level down since that will make the 25 ppm chlorine level much more effective. This is more important than trying to get the pH level down.

The difference in chlorine effectiveness between a pH of 8.0 and a pH of 7.5 at your chlorine and CYA levels (assuming CYA 100 is correct) is only 12% so that's why I say that it is your absolute chlorine level that is much more important than trying to get your pH or TA down right now.

As for any worry that a chlorine level of 40 ppm might be dangerous somehow, this level of chlorine is equivalent to having only about 0.5 ppm of chlorine without any CYA so is not particularly high. This is why I suggest doing the drain and refill because if you get your CYA down to 50 then a chlorine level of even 25 ppm is equivalent to 0.75 ppm without CYA and 40 ppm would be equivalent to 3.2 ppm without CYA. So, getting the CYA level down really leverages the chlorine effectiveness when you ramp up to high levels of chlorine.

After you are through with getting rid of the algae, you should abandon your use of Tri-Chlor pucks (tablets) as your regular source for chlorine and switch to the BBB method or use the liquid chlorine if you found an economical source.

Good luck and hang in there. You will conquer your algae problem if you just stick with the high chlorine (keeping it high through the day and night as much as possible).

Richard

[PoolInMich]

FC 28
CC 0
TC 28
pH 7.6
TA 200
CH 220
CYA 80-85

Water is clear, not crystal clear yet, but wonderfully better. I had to keep FC over 40 for 2+ days to see significant improvement. Brushing daily helped also. Once all the stuff started filtering I had to backwash several times as pressure rose. That led to fresh water being added which lowered CYA. Dry acid has helped maintain pH and slowly lower TA. Now that algae is basically gone I can focus on getting CYA to levels where lower chlorine will maintain it.

Keep posting success stories as they will encourage others like me to persist in following the wisdom in this forum when patience begins to waver.

[duraleigh]

It looks like you've done nice work clearing your pool. You are apparently gaining a good grasp of the issues and acting on them correctly.

Just a cautionary note on your chlorine levels....40ppm could be endangering your liner....perhaps causing it to fade. If you need to shock in the future, I think you would do better to make your target Chlorine about 25-30ppm.

[chem geek]

Given the 75-80 CYA level, an FC of 40 still only generates about 0.6 ppm of HOCl (see this table for some values going from FC to HOCl and this table for some values going from HOCl to FC similar to Ben's chart if you look at the 0.03 as "min", 0.06 as "max" and 0.5 as a possible "shock") so assuming that this disinfecting form of chlorine is what fades vinyl liners, then even an FC of 40 is likely to be safe. Nevertheless, it's probably not worth threatening a vinyl liner just because the chemistry shows disinfecting chlorine levels that are even lower than when if you didn't use CYA. It is possible, though unlikely, that the chlorinated cyanurates (that is, the chlorine bound with CYA) may have some destructive capability to vinyl liners, but I doubt it.

It may turn out that up to 0.5 ppm HOCl is needed to truly kill algae in which case we may be updating Ben's table in the future, increasing "shock" chlorine levels at higher CYA (and possibly lowering the minimums needed at lower CYA, though more chlorine would probably just make the algae kill go faster so isn't a bad thing, up to a point).

Anyway, I'm just throwing in my two cents in. I can't prove my assertion (with regard to vinyl liners) without an experiment.

Richard

[CarlD]

You've gotten good advice, but with CYA at 100, in a vinyl pool you don't want FC above 25 (of course, with the too-high pH it was probably a good thing).

Now that CYA is in the 80-90 range and pH is 7.6, don't push your FC over 20ppm.

filter 24/7, vacuum to waste and brush everyday.

Just keep adding P.O.P.P.--Pool Owner Patience and Persistence.