Partial to full pool drain

Yorker

Silver Supporter
Apr 22, 2017
387
Cathedral City, CA
Question: I’m intending on doing a partial or full drain of our in-ground plaster pool due to the high CH (850). PoolMath suggests a 82% drain to get my CH to 350. (my fill water is 240 CH). I’m not concerned about how long it will take. I have 50’ of pool hose (1 9/16" inner dimension), and a 50’ garden hose (5/8” inner dimension).

1 - I assume I have nothing to worry about regarding the water table since we live in the desert. Am I correct?

2 - Would there be a problem to connect these two very different sized hoses in regard to the different volumes of water that would pass through them?

Here’s some additional information that may help:

The pool is 30’ long x 9’ wide with 2 deep ends (one on each side). There is a 6’ rise from the bottom of the deep end to the top of coping, then 50 to 55’ horizontal to the sewer pipe.

If I read it correctly, my pump states that the Max Flow Rate is 3566 GPH, and the Head Max is 9m (=29’?)
 

Attachments

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
22,031
Laughlin, NV
During the summer, you should not drain a plaster pool in the desert. The sun and heat can crack and damage your plaster.

You can exchange some water without draining.

If you place a low volume sub pump in the deep end and pull water from there while adding water in the shallow end (through a skimmer or into a bucket on a step so you lessen the water disturbance) you can do a fairly efficient exchange. That is assuming the water you are filling with is the same temperature or warmer than your pool water. If your fill water is much cooler than your pool water, then switch it. Add the water to the deep end (hose on bottom) and pull water from the top step.

The location of the pump and fill hose may change if you have salt water, high calcium, etc.
In my pool, with saltwater and high calcium when I drain, I put the pump in the deep end and hose in shallow end. The water in the pool weighs more per unit volume than the fill water from the hose.

Be sure to balance the water out and water in so the pool level stays the same. Also be sure your pool pump is disabled during this process. Once started do not stop until you have exchanged the amount of water you wish.
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
22,031
Laughlin, NV
Read the above. You have high CH and Saltwater. So put the pump in the deep end. You have a spa. So drain that first (be sure all your valves at the pad are turned so they are off to the suction side and the return side) and then use the spa to add the fresh water.
 

Yorker

Silver Supporter
Apr 22, 2017
387
Cathedral City, CA
Thanks Marty, I had read your water exchange method in a number of the posts I reviewed in my research. Since I need to replace over 80% of the water to get to 350 CH, I would assume that will take up a lot more fill water to achieve that .. right?

Not that it matters, but you referenced that I had high levels of salt, currently the Taylor Salt test is measuring 3600 so that is not too high … right?

Would one of my options be to just wait until Oct and do the drain/refill then? IF you think I should not wait that long. I still have the question about connection two different size hoses to the sump pump.

I have 50’ of pool hose (1 9/16" inner dimension), and a 50’ garden hose (5/8” inner dimension).

Would there be a problem to connect these two very different sized hoses in regard to the different volumes of water that would pass through them?
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
22,031
Laughlin, NV
You can connect the two hoses. The smaller one will dramatically restrict the water flow.

Because of your salt and CH levels, the displacement will be fairly efficient. You might have 5% mixing.

I think you can manage your CSI until fall. It is a dance. But with diligent management of pH and TA, it can be done.
 

Yorker

Silver Supporter
Apr 22, 2017
387
Cathedral City, CA
You can connect the two hoses. The smaller one will dramatically restrict the water flow.

Because of your salt and CH levels, the displacement will be fairly efficient. You might have 5% mixing.

I think you can manage your CSI until fall. It is a dance. But with diligent management of pH and TA, it can be done.
I've been keeping my CSI between -2 and +2 by adding MA daily or every two days. But if you think because of the fill and drain water won't mix much ... I'm going to give it a try in a few days. I'll post an update when I'm done. Thanks Marty.

York
 
  • Like
Reactions: mknauss

Yorker

Silver Supporter
Apr 22, 2017
387
Cathedral City, CA
Finally an update. I waited until our CH reached 990 to do the drain/refill water exchange Marty recommended. My fill water's CH was 350. Pool Math recommended a 100% refill for a target of 350. My calculation was 27 hours based on how much water the sump pump took out (360 gal per hour and our pool/spa is 9700 gallons). One problem was that my fill hose kept filling faster than the sump pump was draining, but my solution was to turn off the fill water when it reached the bottom of the coping, then allow the pool to drain 6" to the bottom of the tile before turning the fill water back on. It turns out my CH was only reduced to 500, not as much as I hoped for, but certainly much better than 990.

I'm adding between 16 and 48oz of 14.5 MA daily and having a real problem getting my pH below 7.5 to get my CSI below zero (7.5 gets me to .01 and Pool Math suggests 7.3 to get to -.18). I add the suggested MA, but the pH test just does not budge.

Any suggestions?
 

Yorker

Silver Supporter
Apr 22, 2017
387
Cathedral City, CA
My TA was at 100 after the water exchange, two days later (yesterday) it was 90, prior to the water exchange it had lowered to 60.

Yes, those are the numbers that I enter in Pool Math (or remain from my most recent TA testing)
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
22,031
Laughlin, NV
My TA stays at about 80 ppm with adding 8 oz of 31.45% MA twice a week. I typically test 7.5 or so pH and lower to 7.2. That keeps my TA steady. This is during the high evaporation rate period (May - October). Yours should be relatively the same, adjusted for pool volume and weaker acid.

I would spend a few hours one day and add your acid to lower to 7.2, circulate, test after 30-45 minutes, add to get to 7.2, etc until the pH is 7.2 when you test.
 

Yorker

Silver Supporter
Apr 22, 2017
387
Cathedral City, CA
Thanks Marty, I'll do that today!

Though I do have a question that has always perplexed me. I generally run the pump at 2700 or 3000 for two hours before testing from another area of the pool from where the MA was introduced. I know ...I've read here on TFP that testing after as short as 20 was ok, but how it it possible that the MA fully circulates for an accurate test... even 2 hours at 3000rpms for 10,000 gallons?
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
22,031
Laughlin, NV
It disperses more than circulates. The acid is Hydrophilic, so it seeks to mix with water.

That is why you do not need need high flow rates or long circulation times.
 

Yorker

Silver Supporter
Apr 22, 2017
387
Cathedral City, CA
45 min since adding the 44oz of MA, and the pH tests right at 7.5. So, Pool Math suggests 31oz MA to get to pH 7.2.

Just before this, Pool Math suggested 44oz to get to 7.2. This seems typical though, I always need to add more MA to meet my target than what Pool Math suggests
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
22,031
Laughlin, NV
That is odd. My additions are spot on.

It does not appear you use the Poolmath app. I was going to check your data but it is not shared.
Post your latest full test results.
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
22,031
Laughlin, NV
Your test data is not showing yet. You might need to log out of the site and back in to get it to show.

Good the pH is down.