Algae growing and chemicals in disarray

[hatimtai]

Hi, I am a recent pool owner, built our first pool just 6 months ago. Since then, we hired a pool maintenance company, but just recently got rid of them because they weren't doing anything and were messing up the chemical balancing in our pool. I wanted to use them while I learned how to take care of the pool myself.

Current Problem: Algae growth (2nd time in 3 months) and high CYA/stabilizer

We have algae growing in our pool for the second time in the past 3 months. I wasn't sure why at first, I knew the pool chemistry was off, but wasn't sure where to start. I've now determined it's most likely due to the CYA/stabilizer being too high. I want to start fixing it, but not sure which steps I should take first or which order I should do them in, so any help would be appreciated. I've posted my questions and details about the pool below, as well current chemical levels.

Questions:
1. Should I partially drain and refill pool first to lower CYA levels, or shock pool first? or something else entirely?
2. What can I do to maintain my CYA levels and keep them from going high again in the future? The old pool maintenance company told me that chlorine pucks have stabilizer in them by default, but I would like to not have to do a partial drain every so often.
3. What can I do to prevent algae growth again in the future?

Pool Details and Chemical Levels

Pool Type: Plaster/Gunite/Concrete
Size: 21,000 gallons
Location: Tomball, TX
Water Temperature (roughly 80-95 degrees F in the summer)

Pool Chemical Levels as of 7/1/23
Free Chlorine: 0 ppm
pH: 8 (or higher)
Total Alkalinity: 200
Calcium Hardness: 80
CYA/Stabilizer: 80-90

 

[HermanTX]

Welcome to TFP. You have come to the right place to take control of your pool chemistry.
How did you get the stated test values? You need a proper test kit.
Test Kits Compared

The high CYA and low chlorine level is the cause of your algae.
Stop using pucks and switch to liquid chlorine.(LC) That provides only chlorine to your pool with no added stabilizer or calcium.

The only way to reduce CYA is to drain your pool. You do not want to SLAM your pool with a CYA of 90. If we can believe your CYA of 90 then you need to drain 50% of your water. Actually it may be best to drain 60% because you have algae and you want to CYA to be no higher than 40.

Once you refill your pool, only use LC. Suggest you purchase at least 10 gallons to start as you need then to address the algae. You will require to maintain a FC level of 16 to kill and remove all algae. Assume CYA of 40 but this needs to be confirmed after your refill. Please read
SLAM Process

So in summary
Stop using pucks
Purchase a proper test kit
Drain at least 60% of your pool water to reduce CYA.
Purchase at least 10 gals of LC to prepare for the SLAM process.
Once pool is refilled, start SLAM but you must have a proper test kit to do the SLAM monitoring.