100 Cyanuric Acid Level

[christyne]

Hello. I am a new user in Austin TX looking for advice. A year ago we totally drained the pool (18,000 gallon gunite) because of really high CYA. We bought the house and the pool two years ago. When we drained it, we had it replastered and refilled.

Now have some yellow algae and took a sample to our local pool store yesterday. They said all levels were good except phosphates and recommended adding PhosFree.

My concern is that on their test report CYA is 100. It was not discussed. We began using dichlor tabs and shock about 3 months ago, before that just regular chlorine tabs and shock. It has only been a year since it was drained and refilled.

Why would CYA be high again? Should we just drain a fourth of the water and refill? Thanks in advance for advice and ideas.

[waterbear]

Dichlor does not come in tabs but is sometimes sold as a shock. Trichlor is sold as both tabs and shock. The reason your CYA is high agian is because you are using trichlor and dichlor. Trichlor adds 6 ppm CYA for every 10 ppm chlorine added and normal chlorine loss in a pool is aobut 2 ppm per day so in a month you have added 36 ppm . Dichlor is even worse. For every 10 ppm chlorine addid you are adding 9 ppm CYA! If you use exclusively dichlor to chlorinate and assuming the same 2 ppm per day chlorine loss you have added 54 ppm CYA in a month! Both trichlor and dichlor are acidic on use, trichlor extremely so and it can damage pool surfaces and equipment if proper care is not taken.

The only way to avoid this over stabilizaton is to use an unstabilized chlorine source once the CYA level is where you want it. There are three of them"

Sodium Hypochlorite -- liquid pool chlorine and plain unscented laundry bleach, They are exactly the same thing anf sometime even the same strength. Pool chlorine comes in 12.5%, 10% and 6%. Laundry bleach in 6%, 5.25% and about 8.25% now. Salt water chlorine generators also add sodium hypochlorite to the water. It has very little impact on water chemistry in the long run and is bacially pH neutral on use

Calcium Hypochlorite --usually sold as pool shock but also as chlorinating granules and tabs. The tabs are not meant for use in feeders or floaters but must be used in the skimmer and they do not last long. For every 10 ppm chlorine added it will increase calcium hardness by 7 ppm and is basically pH neutral on use.

Lithium Hypochlorite-- a fast dissolving powder that is sold as a shock. Has very little impact on water chemistry and is basically pH neutral on use but it is extremely expensive to use.

None of these can be used in a tablet feeder or floater but liquid chlorine or bleach can be added with a peristaltic dosing pump system. They are not that expensive but do require regular maintenance.

[christyne]

You are right, my mistake. We are using trichlor tabs and dichlor shock. The guy who replastered the pool said to use the dichlor so it wouldn't bleach out the color of the plaster. Now that the CYA is high again, how do I get it back down to normal range? Thank you.

[waterbear]

Chlorine is chlorine and chlorine can bleach colored plaster. This is why I like sodium hypochlorite, It is a liquid and you just pour it slowly into the return stream and it mixes quickly. If you are using cal hypo the predissolve. If you can afford lithium it dissolves as fast, if not faster than, dichlor. If you have a cartridge filter or a non backwashing DE filter then your pool is going to continue to overstabilize if you continue to use trichlor in a short time. If you have a backwashing filter it will take a bit longer but it will happen.

The only way to lower the CYA is by replacing some of the water. Period. Once you do consider giving up on the trichlor and switching to liquid chlorine or bleach (liquid pool chlorine is not available in all areas but laundry bleach is!) You will have to add some every day or maybe every two days at sundown (depending on the chlorine loss and usage of YOUR pool) but it only will take you 5 minutes or less a day and you should be putting that much time in anyway!

[christyne]

thank you, waterbear.