Cartridge and Tri-chlor and algae, OH MY!

[Texastea]

So, I'm new to pool ownership and made what I now know to be a huge mistake. I have been using Tri-chlor as my sole source of chlorine. Well, it was all going fine until this week when I came home from a business trip and found my pool in terrible condition. Green and Yellow algae.

I upgraded to a better kit (DPD only, no FAS ) and my results are below. First off, I have no idea why the kit says there is 5 ppm of FC. How could that be with the pool in such terrible shape??? Anyway, the CYA is waaaaay to high, so I intend to drain 70% of the pool, refill and if CYA is in the 40 ppm, go from there. The calc says once I get my CYA under control, then I need to add ~6 96oz jugs of bleach and 3 lbs of borax, no?

Anyone have any idea on the funky test result?

FC - 5
CC - 0
pH - 7.3
TA - 120
CH - 370
CYA - 140 at least!!

 

[linen]

Welcome to tfp, Texastea

You can get the fas-dpd test to add to your test kit...you are going to need it. tftestkits.net carries it.

How did you get the cya of 140? That test can really only test up to 100 without dilution, so your cya might be much higher.

First off, I have no idea why the kit says there is 5 ppm of FC. How could that be with the pool in such terrible shape???

Well if you cya was 140 ppm you would need to maintain a minimum of 11 ppm FC to ensure you remain algae free. See: http://www.troublefreepool.com/pool-school/types_chlorine_pool

Per the drain/refill, I would get a more accurate cya value by mixing half cya free water (tap water is fine) and 1/2 pool water and repeat the test, then multiply your result by 2. You do need to be careful you don't float your pool if you have a high water table.

After your drain/refill you will need to do the SLAM process. See: http://www.troublefreepool.com/pool-school/shocking_your_pool

 

[Texastea]

Thanks for the Hello!

The 140 was just an estimate. The black dot disappeared a good 1/4 inch before the 100 line. I'll have to try the dilution trick. Just out of curiosity, does the FAS test do something that the DPD doesn't or is it just more accurate/precise?

 

[linen]

DPD test only goes up to 5 ppm FC (10 if you do a dilution, but the accuracy suffers). The FAS-DPD can go up to 50 ppm FC with good accuracy AND it is counting drops instead of matching colors.

 

[Charlie_R]

The FAS-DPD test is more accurate, and can test as high as 50 ppm FC. Depending on the sample size you can have .5 ppm resolution (10 ml sample) or .2 ppm (25 ml sample). Most here use the 10 ml, as this uses less reagent.

 

[Texastea]

I see. So I'll need that to be sure I have gotten up to the very high FC levels that will be needed to kill the Yellow algae, as well as do the OCLT properly, right?

Also, while we are fairly close to the water table my pool is concrete-plaster. It shouldn't float should it?

 

[jblizzle]

It could certainly float out of the ground if the pool water gets to be too far below the ground water level.

You are correct about the required attributes of the FAS-DPD test to properly SLAM and do the OCLT.

 

[woodyp]

Being in Houston, I wouldn't drain that pool down more than a third at a time. Refill, and repeat.

 

[Texastea]

I'm draining ~1/3 as we speak. Looks like heavy rain is coming in so I might cut it off if that starts. It's about there anyway and I'd almost miss that fantastic shade of algae green in my backyard!