Cya > 300ppm, FC 4ppm, crystal clear pool

[Tmuthart]

Hoping someone can explain why, with my CYA level being as high as it is, I am able to maintain a crystal clear pool with a FC of about 4ppm. Never once had algae growth, pool always looks fantastic. I don't add any chemicals other than a few chlorine tabs each week and a pound of shock once or twice a year. Even throughout the 115 degree Phoenix summers.

I'm using a Taylor K2006 kit to test. The CYA turbidity test, both doing it as recommended and diluting it 2-fold, is amazing. The black dot disappears with only a few DROPS of the water/reagent mixture (literally 4 or 5 drops). Could something else be causing a false reading - making the water more turbid and tricking me into thinking my CYA is much higher than it actually is?

Calcium is high, alkalinity is high (sorry, don't have the numbers off hand, I can get them if it helps), pH is 7.6. Only complaint is the water tastes dull, probably cause there's more CYA than water in my pool!

12000 gallon pool, variable speed pump running 7 hours per day (3.5 hours at about 3000rpm, 3.5 hours at about 1000rpm), cartridge filter, in floor cleaning system.

I really want to switch to the BBB method. Get the pool drained, get the CYA to a more comfortable 50-60ppm, cut out the trichlor tabs. But I'm wondering why fix what's not broken. And why my pool isn't green with the CYA/FC ratio I have going on.

Thanks in advance. Always get great info from you guys.

 

[JasonLion]

Welcome to TFP!

Most likely your phosphate level is naturally very very low, preventing algae from growing. That can keep the water clear, but does not guarantee that the pool is safe to swim in.

The CYA test is fairly reliable. Your experience suggests that the CYA level is really really high. There is a remote chance that you are seeing some kind of interference, but something else would have to be off the scale high for that to happen and usually that would show up in other ways.

It would be good to get specific numbers for TA and CH. Having both high at the same time might be enough to put you at risk for calcium scaling. In Arizona, it is also good to know your fill water TA and CH levels.

 

[BoDarville]

Welcome to TFP.

Hoping someone can explain why, with my CYA level being as high as it is, I am able to maintain a crystal clear pool with a FC of about 4ppm.

The short answer is you have been fortunate so far. Maybe your specific location is not as susceptible to algae compared to others, perhaps your phosphate level is unusually low, and you may not get much plant-based debris falling into your pool - lot's of other factors play in. Eventually, that luck will run out and when it does, your pool could turn green overnight. I've seen a few similar posts over the years with pools having a CYA of 200 ppm or so and the owners stating that they have clean, clear water. It is just a matter of time before that all falls apart. For some, it will happen sooner rather than later.

Although your pool water appears "clear", it is possible that you could have organic contamination of some other kind that may not be visible. That could be part of the reason your water has a "dull" taste. Chlorine provides protection from several kinds of undesirable organisms/microbes - not just algae.

While your testing seems to confirm very high CYA readings, how old is your CYA reagent and where is it stored?

Calcium is high, alkalinity is high (sorry, don't have the numbers off hand, I can get them if it helps)

Yes, it would. Always helps to have as complete a picture as possible in order to provide the best advice.