Persistent Algae

[Kdebelius]

First post. Just received the TF-100 test kit yesterday revealing some troubling numbers:

FC 6.5
CC 0
pH 8.2
TA 240
CH 975
CYA 120 (the cylinder is calibrated only to 100 - my estimate)

I would like to SLAM to get rid of some low level but persistent algae, but suspect it would be difficult with these numbers, especially CYA and am looking for suggestions.

In spite of the algae, water is basically clear.

Thanks for your help. Great site.

 

[jblizzle]

Welcome to TFP!

You can start the cya test with half pool water and half tap water, then the reagent and do the test out side in bright indirect light with tube at your waist. Then double the reading to get a better idea of the CYA level.

Then you need to replace water to get the CYA back in range if you hope to keep the pool clear.

That CH is also very high and needs to come down, also by replacing water. With that high pH and TA, calcium scaling likely.

 

[Casey]

You're going to need to do a few drain/refills to bring the CYA down.

 

[Richard320]

You really have no choice but to drain a bunch of water. It looks like the wells near Burbank run about 90 feet, so I doubt there will be any danger of floating the pool.

The good news is, now that you have a kit and some understanding, algae will be a thing of the past. Too bad you had to pick a drought year to get algae. Pump what uou can onto your lawn. The neighbors lawns, too. Better than just sending it all down the drain.

 

[Kdebelius]

Thanks Jason, Casey and Richard for your comments and ideas.

Repeated the CYA test with half tap/half pool water and doubled, a good idea. Got the same number....60 x 2=120. It is a bit subjective so had my wife try and she also landed at about 120.

So my next question is: How much of the 25,000 gal would you recommend that I drain?

BTW, my wife just checked the current Burbank rates and 15,000 gal (for example) is looking like about $60.

Yes, bummer to have to do this in a drought!

 

[jblizzle]

If you have no ground water concerns, then you want to replace about 2/3 of the water to lower the CYA to about 40ppm.

 

[Kdebelius]

As suggested, we drained about 2/3 of the water and replaced with the city of Burbank "blend". I noted that my local water registers CH at 325 and TA of 180 with a ph around 8.2.

With the refill complete, I SLAMmed and passed the OCLT.

Before I get to the question, here are the current numbers:

CYA: 52
ph: 8.2+ (a bit high, I know)
CH: 650
TA: 210

We have been using 10% liquid chlorine ONLY to attempt to maintain a target FC of 7. Have not used any other chlorine products.

What we are noticing is that we consistently drop to FC of around 3 on a daily basis. Is this normal? This has been going on for a couple months. Seems like we are using quite a bit of chlorine to keep this 25,000 gal within the acceptable range.

The CC is always below .5, many times at 0.

Thanks for all your help.

 

[tim5055]

You have a good sized pool and 2ppm loss per day is not unheard of.