FC low with SWCG. Advice?

[chrishick]

Your CYA will not go up on its own. It has to be testing error.

Was the lighting different from one CYA test to another. It is important to do it in the sun light about the same each time. Read up on testing CYA in other threads....

Your SWG will always have a difficult time "catching up" unless it is way oversized. Use bleach to bring up the FC level needed and then let the SWG maintain.

But will CYA drop 30ppm in a week without a water change? If my testing is accurate then where did it go?

I've read everything I can find on CYA testing and I'm sure I'm doing it right, but for me it is the most difficult test to read.


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[mgmoore7]

CYA is the most difficult test of all of them. It won't drop without water replacement and it won't increase without the addition of CYA.

Did you add any CYA 3-4 days or even a week before the time you tested? If so, how did you add it?

I would suggest that you test it today in full sun. Hold the tube with your fingers at the top. You can move it in and out of direct sun to see the difference. Most recommend to have the sun to your back and the tub in the shade of your body. A difference of 10ppm from one test to another is not going to make a huge difference, but 20-30 or more can.

Also, someone else suggested that you fill a graduated cylinder with pool water to 15ml and then the CYA reagent to 30ml, then pool into the mixing bottle. Some of us has found using the mixing bottle for the measurement to be a little hard to get amounts just right. This method bypasses that issue where you may add a little too much or too little of the water or reagent. I have found this method to provide more confidence that I have the right amounts.

Do you have the 50 ppm standard solution? This can help know what 50ppm looks like.
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