Closing an In-Ground stability probs

[average_joe]

Hi Folks,
I've been taking care of our pool for a couple years with no problems, but this is my first time closing. The biggest problem is I haven't gotten much sleep the past couple days because of a bad back, and my brain just isn't working right now.
I'm also under a time crunch- the winter cover is folded up and laying on the concrete next to the pool and it needs to get opened up and put on before it starts to mildew.

Pool is concrete in-ground 26'x22', 7 foot at deepest end, 3ish at other end. Approx. 22,000 gal

Water Temp: 61
Free Chlorine: 3
Total Chlorine: 3
Combined Chlorine: 0
pH: 7.8
Alkalinity: 70
Calcium Hardness: 160
Cyanuric Acid: 90

I would use Muratic acid to decrease pH, but that will also lower the Alkalinity even more. What should I add first?

 

[domct203]

Hi Folks,
I've been taking care of our pool for a couple years with no problems, but this is my first time closing. The biggest problem is I haven't gotten much sleep the past couple days because of a bad back, and my brain just isn't working right now.
I'm also under a time crunch- the winter cover is folded up and laying on the concrete next to the pool and it needs to get opened up and put on before it starts to mildew.

Pool is concrete in-ground 26'x22', 7 foot at deepest end, 3ish at other end. Approx. 22,000 gal

Water Temp: 61
Free Chlorine: 3
Total Chlorine: 3
Combined Chlorine: 0
pH: 7.8
Alkalinity: 70
Calcium Hardness: 160
Cyanuric Acid: 90

I would use Muratic acid to decrease pH, but that will also lower the Alkalinity even more. What should I add first?

Welcome to the forum. Sorry to hear of your back issues, I hope you bounce back quickly.

What are you using for a test kit?

There are guidelines to closing an inground pool listed here.

It's fine to lower your pH with MA. Once you reach your pH target, you can use baking soda to raise TA if needed with very little effect on pH.

Your pH is not that high, lowering to 7.5 should have minimal effect on your TA so you could address that in the spring.

Once you have your pH where you want it, you should raise your FC to shock level and maintain until you can pass an OCLT. Unfortunately with your very high CYA level of 90ppm your shock level is 35ppm. Once you pass the OCLT you can let your FC drift down to about 15-20ppm and optionally add a polyQuat-60 algaecide and run the pump/filter for 24 hours to mix thoroughly. This should all be started days before you plan to actually cover the pool.

How did your CYA get so high? Are you using Trichlor pucks or Dichlor granular to chlorinate the pool?

Also, a FC of 3ppm is too low for your CYA level. Your FC target is 10ppm for that CYA level, with the minimum FC at 7ppm.

HTH,
Dom

 

[average_joe]

Thanks, Dom.
I use a Taylor K-2005 test kit. CYA is high because I've been using Dichlor the last couple weeks. I usually use Cal Hypo.

 

[domct203]

Thanks, Dom.
I use a Taylor K-2005 test kit. CYA is high because I've been using Dichlor the last couple weeks. I usually use Cal Hypo.

The Taylor K-2005 is only good up to a FC of 10.0ppm.

For every 10ppm of FC added with Dichlor, you also add 9ppm of CYA.

Why did you stop using Cal-Hypo? Your CH is still too low and should be at least 250ppm.

You should return to Cal-Hypo (or use another source of calcium) until you reach 250-350ppm, then switch over to liquid chlorine, aka bleach.

Hot to chlorinate your pool

You should also lower your CYA by draining & refilling to dilute. Unfortunately this will also lower your CH.

You can wait on the CYA until spring, but you should really address the CH now as to not cause damage to your plaster.

If the pool develops algae at that high of a CYA it will be extremely difficult, time consuming, & expensive to address at a CYA of 90ppm. Don't make large water exchanges unless you know your water table in your area. A high water table could pop a pool right out of the ground, like how a half full cup of water will float in the pool. A 50% drain then refill would get you to about 45-ish ppm, but as I said earlier it is much safer to make smaller, multiple drain & refills eg. three-four 20% exchanges or 7-8 10% exchanges.

Dom