Partial to full pool drain

Yorker

Silver Supporter
Apr 22, 2017
376
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’?)
 

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mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
21,235
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
21,235
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
376
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
21,235
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
376
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
 
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