What to do?

[bill5416]

Over the last several weeks had a pretty good bout with mustard algae. Had to raise the clorine level up per the calculators instructions but everything soon began to clear up nicely. Upon returning recently from out of town I found the water crystal clear and looking as good as it ever has. Hadn't tested in a while so I decided to check my readings.
FC - 19 - Still really high since the shock with bleach but auto clorinator still runs with filter on
PH - 6.8
TA - 50
CH - I don't get any reading at all
CYA - 90+ wanted to test again but reagent too low

I am beginning to doubt some of my readings. Test kit is a year old but DPD powder looks dark and Calcium hardness test wouldn't begin to turn water red. just went and bought some baking soda to raise PH and TA. Never had to add calcium since I've had the pool but never go a zero reading either. Any siggestions? Hard to understand the need to keep treating when the pool looks great.

 

[Vette]

Keep in mind baking soda raising TA much more than it does PH.

You have a TF-100, no? Refills for that are availible from their website. tftestkits

 

[jblizzle]

With your very high CYA, you are going to have to be careful maintaining the correct FC level which is a MINIMUM of 7ppm so that you do not get a green pool. If the algae happens, the first thing we are going to tell you is to replace half of your water to lower the CYA into the recommended range.

Also, if you are still using the pucks in the chlorinator (which is likely the reason your pH is so low), you are still adding to your CYA levels. So your required minimum FC level is going to keep rising.

One of the problems maintaining high CYA levels and thus high FC levels is that the pH test is not valid when the FC is greater than 10ppm ... if you have to maintain your FC that high to avoid algae, then it becomes hard to track the pH.

WHOA ... which just reminded me that it reads falsely high ... so that likely means your pH is probably MUCH lower than 6.8 since you have high FC currently.

 

[Vette]

I'm using Trichlor to add CYA right now and it amazes me what they do to PH. Those tabs have a PH of like 2.5 and they are NASTY. I'll add Borax up to 7.8 and it will be 7.2 in a few days. And that's with low chlorine use, our pool gets a lot of shade. Someone who burns through tabs quickly can have a dangerously low PH on their hands. I test my PH everyday and have that problem. It scares me that many people do their once a month pool store tests and just add Trichlor tabs between pool store visits.