High CYA level - what to do first?

[timd]

Good afternoon all,

Had my water tested today at the local pool store, below were the results:
Free Chlorine - 0
Total Chlorine - 0
CYA - 90
PH - 7.5

I have green algae in the pool and have been struggling with it the last couple of weeks. Added 1 bottle of bleach (pool essential chlorination liquid 10%) from Wal-Mart last Saturday. Pool looked better on Sunday, but now have algae again. I think I need to lower my CYA from reading other posts, would that be the 1st recommendation from the experts here?

Will fix my signature, but have a 14,500 gallon in-ground pool with inline chlorinater filled with tablets.

 

[jblizzle]

Welcome to TFP!!!

Step 1: forget about the pool store tests and invest in one of the Recommended Test Kits
Step 2: add 1/2 bottle of 10% chlorine every day until you have your test kit.
Step 3: Test your water
Step 4: Depends on your test results

 

[mknauss]

Welcome to the forum!
Read Pool School - ABCs of Pool Water Chemistry

Download Trouble Free Pool School

Once you get your test kit we are all here to help!

 

[timd]

Have read the Trouble Free Pool School and ordered a TF-100 test kit that should be here next week. I will continue to treat the water with liquid bleach until my kit arrives then follow up.

 

[ctrav]

Welcome to TFP and good job reading...

As suggested this is very important:

ABC’s of Pool Water Chemistry

 

[timd]

I received my test kit yesterday evening, feeling like a mad scientist now! Over the weekend I brushed the pool, and added 1 bottle of 10% bleach and let the pump run overnight. Sunday morning it looked much better, still a small bit of algae on the bottom, backwashed the filter and then drained about 3 feet of water from the pool. Replaced the water (ran for almost 9 hours) and have been adding 1/2 bottle of the 10% bleach daily. Tested water yesterday, below are my numbers:

Free Chlorine - 1
Total Chlorine - 1
CYA - 120
PH - 7.8

I have added 1/2 bottle of MA this morning and will test again this afternoon to see if PH has come down a little as recommend by pool math app.

By my calculations, with the high CYA level, I should add 5 bottles of 10% chlorine to bring it to shock level. I don't mind spending the money on chlorine to keep it higher, just don't want to have to drain and fill the pool even more to get the CYA level back down.

Am I on the right track, and does anyone else have any other suggestions?

 

[wkussmaul]

Hi, I'm not an expert, but I got mustard algae in my pool a few years back after 3 years of using pucks for chlorine. What I didn't know is that the pucks slowly add CYA to the pool water; eventually my CYA level was high enough that even with "correct" chlorine levels (using my test kit), the free chlorine was not able to be active, thus allowing the algae to grow.

I killed the algae, backwashed the filter, and stopped using pucks except during vacations. I listened to what the experts told me on this forum, bought 12% bleach in carboys and have used it exclusively ever since. NO algae problems ever again!

This is a great website!!

 

[timd]

I forgot to add, I had been using the pucks for Chlorine also, but I turned that off after reading all the info on this site too. I will only use the pucks if I am not at home for an extended period of time.

 

[mknauss]

It would make much more sense to swap out about 50% of your water. Why are you hesitant?

 

[timd]

I have been debating on doing that, keep thinking about the added expense on the water bill, but in the long run will probably be worth it.

 

[SDor]

With a CYA of 120, unless your water is really expensive, it will be cheaper in the long run to replace the water instead of buying all the extra chlorine you will need to get to and maintain SLAM FC levels. With the pool calculator, look at the difference in required chlorine when CYA is 120 vs 40. For a 15K Gal pool, its 7 gal (target 47 FC, CYA 120) vs ~2 gal (target 16 FC, CYA 40)... and this is just for the first dose. You will be adding ~3x more chlorine every time you need raise the FC. It adds up.

 

[timd]

Drained the pool yesterday evening, filling back up overnight, it should be back above the skimmers by noon today. How long should I let the pump run before I test the water?

 

[zea3]

Let everything circulate at least 30 minutes then test.

 

[timd]

Tested the CYA level at lunch, still reading about 80. Brushed the pool down really good, will add some bleach tonight and let the pump run overnight. Water is really green, but hopefully will clear up after adding bleach and running for several hours. Any other suggestions.

 

[mknauss]

How much water did you replace? I do not remember if you did the dilute test for your CYA of 120?

 

[timd]

I ran my pump on waste for 1 1/2 hours, I estimate I replaced around 75%.

 

[mknauss]

Did you do the initial CYA test were you indicated 120 ppm using the dilute method? Step 8 in the CYA testing directions in Pool School.

 

[timd]

No, I did not, I was going by the CYA instruction paper that came with my TF-100 test kit.

 

[mknauss]

If you get a CYA reading of 90 or higher, you should do Step 8 in Pool School - CYA

The vial is logarithmic. So if you 'geusstimated' above 100 it was probably 200+. So your CYA of 80 now means you should do another 40% plus drain and refill.

It is no good to use waste for an extended period. Better to get a sub pump. From Harbor Freight or Home Depot, etc.

 

[timd]

Just did the diluted test, shows reading of 60 so if I double that, means my true CYA is 120 now?