What's the correct way to measure and lower CYA?

[gustafson]

I understand the TF-100 CYA test is a bit subjective, but anyone have tips to get reliable results? I, for one, tend to see a faint black dot for quite a while and wonder if I'm going way past and registering low CYA readings as a result. Second, I'm not sure about the protocol for shaking the bottle after the 30sec wait. I give it about 10 vigorous shakes, but wonder if there's a more standard way of doing it.

As regards to lowering CYA, is it correct that it concentrates at the top, so draining the surface water via the skimmer is more effective at lowering CYA levels?

TIA!


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[cowboycasey]

CYA is evenly mixed in all your water...

 

[Divin Dave]

Yeah, we all suffer about the same when measuring the CYA. It takes some getting used to for sure.

The best accuracy for the CYA test is....
do it outside in natural light
Turn your back to the sun
Hold the vial at waist level and despense the solution into the tube.

While you are looking into the test tube, only hold the tube with 1 finger and thumb. Light plays a large role and holding the tube with more fingers blocks out more light. So whatever you do, do it consitently every time.

Dont do it just once... pour the solution from the test tube back into the bottle and repeat the process a few few times. Then take an average.

 

[BuckeyeChris]

perhaps what you were thinking comes from some recommended drain and refill methods, where you have one hose at the top of the pool draining high cya water and another hose at the bottom refilling from the tap at the same time. If your water table puts your pool at risk of floating or shifting when the water pressure is lowered due to a drain, this method will keep the pool full and minimize the mixing of the water to speed up the dilution.

 

[JoyfulNoise]

I understand the TF-100 CYA test is a bit subjective, but anyone have tips to get reliable results? I, for one, tend to see a faint black dot for quite a while and wonder if I'm going way past and registering low CYA readings as a result. Second, I'm not sure about the protocol for shaking the bottle after the 30sec wait. I give it about 10 vigorous shakes, but wonder if there's a more standard way of doing it.

As regards to lowering CYA, is it correct that it concentrates at the top, so draining the surface water via the skimmer is more effective at lowering CYA levels?

TIA!


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CYA is evenly distributed throughout the pools volume. If the pool water were completely stagnant and there was a fairly large difference in temperature from top to bottom, you might see a small concentration change with respect to depth. But, since your pool water is mixing quite a lot and the temperature differences are not that big, you can safely assume the CYA is evenly distributed. Free Chlorine concentration can vary with depth by a noticeable amount because it is strongly affected by UV light, but that's about it.

As for measuring CYA, others have given great advice and I would only add one more thing - try not to shake the tube or tilt it while looking down at it and look down as straight as possible. The curved surface of the water (meniscus) can act like a little lens and make the dot seem to appear and disappear.

 

[gustafson]

Thanks for the input!


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