FC / CYA on refilled water

[gpminz]

Our pool woudl not hold FC and the CYA was 250-300.
We drained the pool about 80%. we have a 20,000 gal, gunite pool.
We started refilling and noticed a greenish color. We have since tested and the pool with a K2006 kit.
FC - 0-.5
CYA< 30 (the black dot was still barely visible when filled to the top of the test tube)
pH -7.5
CH -300

We added clorax bleach at the recommended rate per pool calculator. 2 hours later , no FC.
We then shocked it with Hypo chlorite in the evening, in the morning no FC - however the pool is now very clear.

We have some left over dichlor tabs in the cylinder that we are using to raise the CYA slowly. However we need to get chlorine back in the pool. Can you please give me some suggestions. Should we add stabilizer, or just keep adding bleach until it stays?

Thank you

 

[bridgman]

I would keep adding bleach, since you need to maintain a good FC level in order to kill whatever was growing in your pool.

You can use the tabs at the same time to raise CYA, just add a bit less bleach to compensate for what the tabs add.

BTW I *think* the tabs are more likely to be trichlor than dichlor... I'm asking because dichlor and trichlor add different amounts of CYA.

 

[gpminz]

Thank you - you are probably right -I was guessing on the tabs.
How often or how long should the bleach last. If we put it in and then 4 hours later it is gone add more?
We have been hesitant to add the stabilizer as this is the second year we have drained the pool. Can we count on the tabs to raise it enough?

 

[bridgman]

You can use PoolMath to figure out how much CYA each tab will add, then count out the number of tabs you need to add ~20 ppm of CYA and stop when they're gone, wait a week and retest your CYA level. Typical tabs are 7 or 8 oz of trichlor.

If there is stuff growing in your pool the chlorine will get used up VERY quickly -- recommended practice for a SLAM is to raise the FC to shock level then retest & add more bleach as needed every half hour at first. After a while the FC level won't drop as quickly, and you can move to hourly, then every few hours, then a couple of times a day, then daily once the SLAM is done. Always add more if it's gone, anyways.

 

[RobbieH]

I wouldn't add any more hypochlorite either. Your CH is already 300, you don't want it to go any/much higher.

 

[gpminz]

Thank you - we are learning - I wish we had found this last year. Our first year the chemistry was perfect, never had any issues, but then last year it all started. We are getting ready to add liquid CYA ( i know its more expensive, but I want to get it taken care of and quit worrying about it. )We are adding bleach 8.25%. This morning the FC was 1 and after adding 121 oz of bleach at 6:30 am at noon FC was at 4. The water is crystal clear by the way. I will test it when i get home to see where we are with FC.

After we get the CYA/Cl addressed, we will address the CH issue. One step at a time for us!