New Owner Planning CYA Replacement on Open

[IzzyJRay]

Hi Everybody!

I bought a house last month that's got an awesome pool in the backyard. Gunite pool+spa, about 18000 gallons best as I can approximate, liquid chlorine setup. I'm fully intending to DIY as much as possible. Done a ton of research through Pool School, r/pools, and these Forums! Super happy to be here and part of your community.

On to business...

Water temperatures today was 55F in the pool at 60F in the Spa. Here are the measurements I took with my new TF-Pro test kit.

PH: 7.7
Cl: Off the scale (orange)
FC: 21ppm (43 drops of R0871 counted)
CC: 0
TC: 21ppm
CYA: > 100
CH: 500 (20 drops)
TA: 120 (12 drops)

Pool is not yet open, planning to wait another week or two until things warm up just a hair. That said, I'm trying to develop a strategy for when when I do eventually fire things up.... My CYA is clearly off the charts (attached pic of view cylinder from TF-Pro). I'm guessing it's ~130-150. I guess it makes sense CL is so high... Based on what I know about prior owner, I think they just continuously added Chlorine product with stabilizer included from the pool store over the years, never bothered actually checking stabilizer levels. Water is pretty clear under the cover.

I am hoping to fully embrace TFP methodology, so clearly need to get my CYA down. I've got a few questions I'm hoping ya'll can help with my planning:

• If I'm doing water replacement to get CYA down, is it reasonable to shoot for a target of 60 per TFP recommendation for Liquid Chlorine setup? Or since I'm replacing anyway, should I just target 40? The difference is 50% to 70% water replacement in my setup... I'm feeling guilty about tossing an additional 3600 gallons if it's not absolutely necessary.
• What's the best order of operations here? My plan is to open the pool, double check measurements with pump/filter going, and then immediately start replacing water. Is there any reason to do things differently (i.e. raise FC, fully vac/clear up water, then to get replacement going)?
• Plaster seems to be in good condition with a small amount of cracking. A buddy told me that replacing that much water will totally crumble/destroy my plaster, especially in the desert where I'm at with dry air. Is this true? Should I have any concerns or take any special precautions when replacing 50-70% of my water? Previous owner told me she has never drained/refilled or done a significant replacement in 20 years pool has existed.

Thanks!!

 

[mknauss]

Wait until you can fully circulate the pool for 24 hours and then take a water sample and run a full set of tests.

 

[Newdude]

Hey Izzy and Welcome !!!!

If I'm doing water replacement to get CYA down, is it reasonable to shoot for a target of 60

First things first. Is it well mixed ? It's not open yet but I bet you and me have different views on what is considered 'closed'


If you have the ability to mix, do a diluted test. Use half pool and half tap as the sample. Proceed with the rest of the test as normal and double the result. If still 100+ (which would be 200+) you'll be draining so much it's kinda moot to split hairs.

But yes. 60 CYA is entirely manageable if your drain hits that as the target.

 

[notactjack]

For what it's worth when I had to drain. Half of the pool water did not equal half of the cya gone. I would drain it until it's empty and start fresh. I've drained twice now and I think I'm going to have to do it a 3rd time.

 

[Newdude]

For what it's worth when I had to drain. Half of the pool water did not equal half of the cya gone.

Yes it did. pool = X cya and fill = 0 cya. Half pool / half fill = half X cya.

But. People misjudge the volume drained all the time. Or it mixes too much while doing a no drain exchange. Or there was CYA test error from having sky high CYA and doing the dilution test, which was subjective to start. One way or another, something was off.

 

[notactjack]

Yes it did. pool = X cya and fill = 0 cya. Half pool / half fill = half X cya.

But. People misjudge the volume drained all the time. Or it mixes too much while doing a no drain exchange. Or there was CYA test error from having sky high CYA and doing the dilution test, which was subjective to start. One way or another, something was off.

Granted was just pointing out in practice it didn't work. Subjectivity in the cya test, estimating pool volume etc.