New CPO in over my head with low chlorine levels

[Aquaman87]

I manage a 99,000 gallon plaster in-ground pool with sand filters and I can't recall the flow rate or pump size... both of which have been used on this pool for years. The most recent levels are Cl: 1.0. Ph: 7.6. CYA: 0. TA: 90. Clarity is very clear. Temp is around 83 depending on the time of day. My supervisor, who taught my CPO class, came out with a repairman but couldn't find anything amiss. Several hours ago I added 30 scoops of cyanuric acid as suggested by my supervisor.

I've run the chlorine pump for eight hours several days and cannot get the level up. It peaked at 5 several times but never lasts. The Ph stayed at 8 for several days. I got it down to 7.4 two days ago and tried shocking the pool with several chlorine sticks but again it doesn't last.

What could be killing the chlorine? I've gone through almost half a tank in one week. The pump is working fine. This is my first summer as a CPO. This is the first year with this problem but last year's staff is as stumped as I am.

 

[JohnT]

Welcome to TFP!

Lack of CYA will allow the sun to consume your chlorine very rapidly.

 

[Divin Dave]

The sun is consuming the FC. UV rays destroy it.

 

[BoDarville]

Welcome to TFP!

Dittos to what the other responders have stated.

Although you recently added (presumably) granular CYA, it will take up to a week for the granules to completely dissolve and get fully incorporated into the water. I would retest the CYA level a week after you added the 30 scoops and see where you are at.

If more CYA is needed, I would use the Pool Math tool to help determine your follow-up dose. Input the following information:

1. Pool water volume (99,000 gallons)
2. The most recent CYA test results
3. The desired CYA target

PoolMath will tell you how much CYA to add. We recommend adding the CYA to a sock or old T-shirt (or similar), tie it off, and then place it in the skimmer. Depending on how much you need to add, it may be beneficial to spread the dosage out among multiple skimmers to guard against restricting water flow in any one skimmer.