Imbalanced with algae - last few weeks of the pool season

[italianbreadman]

Hi everyone. I was hoping I could get a little advice.

I had my 6500-7000-gallon above-ground pool balanced where I though was perfect about a month ago.
About 3-4 FC, a pH of 7.4, TA around 100, and CYA at 30-40.

I went away and left my father in charge for a month, and now I’m battling algae and some funky numbers.

I’m using a Taylor K-2006 kit, and I have the following readings:

FC: 16
CC: 0
CYA: 100
TA: 70-80

I also have a pool that looks like the photo as far as blooms are concerned.

I’m not super experienced with maintaining a pool, but I’ve never experienced such odd FC levels with algae like this. Is my chlorine entirely locked in the stabilizer from the trichlor pucks my dad likes to add 2 and 3 at a time in the floater? I thought 16 would be enough and that I’d see some CC with al this organic material.

Am I looking at superchlorinating to 30-40 ppm with liquid bleach?

Do I need to drain half the water (to drop CYA) in order to get back on track?

With only maybe 2 weeks left of decent swimming weather (subjectively), I’m considering throwing in the towel and closing the pool until next year.

I also find it frustrating that I can’t find basic formulas for chlorination online, only “this much of this product at this concentration raises this volume of water this much.” I’m unsure how I would convert, for example, CalHypo into 7.5% Na Hypochlorite liquid, if there’s no basic unit of available chlorine (for water-sanitizing purposes) that we know exists at x per oz in one and y per oz in the other. Is that information available somewhere. I figure if anyone would know, folks here would.

Anyway, any advice would be appreciated. I hope I provided adequate background info. Thanks!

-Ed

 

[HermanTX]

Welcome to TFP. You can certainly find lots of help on this forum.
Just curious - how did your CYA go from 40 to 100 in 1 month? You physically have to add it to raise it such as with pucks or stabilizer additive.
Have you viewed the FC/CYA Levels. This indicates you need to maintain your FC at 11-13 and that is assuming your CYA 100 is accurate. Your FC must have dropped down during the month and caused the algae to form or your CYA is higher than 100.

First I would verify that your CYA of 100 is accurate. There is a dilution method by using 50% tap water and 50% pool water to make up the "pool sample" portion, then add in the matching reagent and test your CYA. Then multiply your result by 2. So if you read 45 in the dilution method your CYA is really 90. However if you read 80 then your CYA is 160. That is why it is important to know the real CYA.

Come back with comments and results.

 

[Richard320]

Welcome!

Start with ABCs of Pool Water Chemistry so we're speaking the same language.

Then follow the video.


If you prefer the book to the movie, this is more detailed. SLAM Process

But be aware that the first step is going to be to reduce the CYA level to something reasonable, which will involve replacing at least half the water. Others have started with worse situations. Check out some of the links here and do what they did. Recovering my old inspirational links

 

[italianbreadman]

The diluted CYA test shows a result of about 110 (the meniscus of the 25/25/50 mix of tap/pool/R-0013 reads halfway between 50 and 60)

I presume CYA got that high through overuse of trichlor pucks. And yes to the chart. That's where I got 40 as the high end of the range I noted about superchlorination. It says for a CYA of 100, the normal and SLAM FC values are 11-13 and 39, respectively, which is why I thought my existing 16 FC would be enough to sanitize.