High CYA Pulled Down With Flocculent?

[dulac87]

I have a 23K gallon inground pool that has had high cyanuric acid levels this year already. The problem is a carryover from last year, which I thought I had fixed by draining half of the water last fall. However, I was told by my local pool store that draining from the shallow end did not provide the full benefit because CYA is heavy and is more concentrated in the deep end of the pool (Has anyone head that?).

Anyway, after not being able to get my chlorine readings to stick, I had the CYA checked and found it to be at 150 ppm. I drained 1/3 of the pool water from the deep end and now have the CYA down to 70 ppm. However, it is still taking more chlorine than normal to maintain a reading. Traditionally I have used di-chlor granular but switched to tri-chlor tabs this year because of the lower CYA content. My pool guy has suggested using a flocculent agent before draining more water because he says that the flocculent will capture some CYA within the solids formed. Does this make sense?

 

[JohnT]

Welcome to TFP.

Your pool guy doesn't know what he's talking about. Drain the water from wherever you want and you'll remove the same amount of CYA. The floc isn't going to affect your CYA either, although if the water is cloudy enough it can make your CYA read high, so using floc could improve the test accuracy.

 

[Guest]

also, using trichlor is not going to have that much of an impact over using dichlor on how fast your CYA rises. Most pools lose about 2 ppm per day of FC that needs to be replaced so in 5 days you have consumed 10 ppm FC. For every 10 ppm of FC added dichlori adds .9 ppm CYA and trichlor adds .6 ppm CYA. Do the math and you will see that both will raise your already too high CYA beyond manageable loimits in a very short time and you will be having problems by the heat of August!


BTW, the reason your Cl reading would not 'stick' is reallyrelated to the CYA level in a roundabout way. Your FC was way too low for the CYA so you always were killing algae which was quickly consuming the FC!

 

[JasonLion]

Both dichlor and trichlor increase the CYA level, which is really not what you want. Trichlor is also bad to use for shocking because is dissolves so slowly you never reach shock level. You need to shock the pool with something that dissolves quickly and doesn't add any more CYA. I suggest using bleach/liquid chlorine.

The other key to shocking is to raise the pool to shock level for your CYA level and keep it there by frequent testing and addition of more chlorine as needed. With a CYA of 70, shock level for your pool is 28. Complete directions on how to shock are here.

 

[chem geek]

For every 10 ppm of FC added dichlori adds .9 ppm CYA and trichlor adds .6 ppm CYA.

waterbear meant to leave off the decimal points. The chemical rules are as follows:

For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.
For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.
For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by 7 ppm.

Even at a very low chlorine usage of 1 ppm FC per day, using Trichlor as your only source of chlorine will increase CYA by over 100 ppm in just 6 months, unless there is significant dilution of the water. At 2 ppm FC per day usage, the CYA increases by over 100 ppm in just 3 months.