Water exchange

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Pennypat

Pennypat

Bronze Supporter
Jul 15, 2016
180
Hiram, GA
Pool Size
26700
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Hayward Aqua Rite (T-15)
I’m in the process of a water exchange. I have had an iron issue for a couple of years. I deduced that the iron was from using Clorox salt. I did a water exchange at the beginning of 2024 in and out method and basing my calculations on the amount of water going in and out and the size of my pool.

When I thought the exchange was complete, I started the pool up and tested for salt and it was at 800 ppm. I thought this was a small amount and probably wouldn’t matter. However, I still had a problem with staining, although it had improved. When I added salt I used Morton Pool Salt. So, I’m not sure if the problem was the residual salt or the Morton salt.

Right now, I’m using my salt level to determine if the exchange is complete. After 3 days of 24 hours of exchange, my salt level is 400 ppm. My question is: Can I actually get the level to zero?

I’m really ready to enjoy the pool this summer.😜
 
Pennypat said:
Right now, I’m using my salt level to determine if the exchange is complete. After 3 days of 24 hours of exchange, my salt level is 400 ppm. My question is: Can I actually get the level to zero?
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The issue with the water exchange and measuring salt is this. For the exchange to be effective, you need to turn the pump off, and figure out the temperature/TDS differential between the pool and fill water to determine where to fill and where to drain. The point is that you want the water to stratify (hence the pump off). So that the water you are draining is the pool water, not the new fill water.

In order to accurately measure the salt content, you then, AFTER you are done with the exchange, mix the water together before you sample and test.

It is best to do the exchange longer than you think/calculate, if you want the best chance at exchanging the most water.

You will likely never get it to zero. By the way, if you use liquid chlorine and muriatic acid, they both add salt.
 
What was your salt level before you began the water exchange?
 
More importantly is the delta T between fresh and pool water. The closer the the delta T meaning, temperature of the fresh water in relation to the water you want to exchange the faster the two mix and then you're at that point not removing only pool water but also the new water. I always recommend to heat the pool water before the exchange for better outcome and that's how I do it.
 
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Pennypat said:
3100 ppm
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Going from 3100 ppm to 400 ppm would say you changed over 85% of your water.

wireform said:
I think you need more pump time to mix well. Your outcome is like 85-90% exchange which is too good to believe.
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That could be.
Pennypat said:
I did all that, other than turning the pump on. How low do you think it is likely to get?
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You will never get it to 0.

It may be worthwhile stopping the Water Exchange, running your pump for 24 hours, and measuring your salt level. This will give you a benchmark for how much water you exchanged in that time.
 

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I’m down to 200 ppm. I’m wondering if there could be enough iron in that salt to cause staining and could I go any lower? Opinions??
 
Did you do an ascorbic acid treatment to lift the stains before water replacement?

Ascorbic Acid Treatment - Further Reading

www.troublefreepool.com www.troublefreepool.com

My guess is that whatever is left as staining can be lifted with an AA treatment. May get away from having to use the sequestrant because of the new water, and likely small amount of iron in the stains. Thoughts @ajw22 ?
 
PoolStored said:
Did you do an ascorbic acid treatment to lift the stains before water replacement?

Ascorbic Acid Treatment - Further Reading

www.troublefreepool.com www.troublefreepool.com

My guess is that whatever is left as staining can be lifted with an AA treatment. May get away from having to use the sequestrant because of the new water, and likely small amount of iron in the stains. Thoughts @ajw22 ?
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Actually we were testing out of the pump hose before running it and after running it a while, it tested 300 ppm. I did do an AA treatment before the exchange and it looks nice right now. I’m going to run the pool pump a while today and retest today.
 
I just wanted to report that my water exchange was a success!!! I have a slight discoloration on my steps that comes off with vitamin C. But, it comes back which is a mystery to me. So, my 3 year iron ordeal is finally over. No more cheap salt for me.
 
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mas985 said:
Have you tested your fill water for iron?
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Yes, I had it sent out through my county. And, I’m getting a little more staining now. But, my chlorine has creeped up to 10😳. I think I’m going to do another AA treatment and keep the chlorine down.
 
I put a bottle of sequestrant in and it lowered the chlorine and it’s looking good. It’s the best it has looked in 3 years. SUCCESS!!
 
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