Exchanging Water after reading draining guide

[pizaul]

I am doing a water exchange to lower CYA as I’ve moved away from trichlor tabs to liquid chlorine a few weeks ago, with the goal to go salt next year. I don’t have any cloudy water or algae as I must’ve gotten lucky with tabs as FC generally was always around 10, just want to get my CYA to the proper range to maximize chlorine effectiveness and follow the CYA/FC recommendations. I read all there is to read in the draining article here but just wanted to confirm with all. My public tap water comes out at 67.5F, pool temperature ranges from 72-76F as we’ve had chilly nights here in MD. So at most the difference is 8.5F. Since this isn’t >20F, should I be pumping from the deep end and pouring in fresh water from my skimmer in the shallow end? I can’t do the DeltaT calculation as I don’t know what my fill water TDS is. I was getting ready to pump from shallow end in the photo, my guess is I think I need to flip this around.

FC 7
CC 0
CYA 100+ on TF-Pro test, 160 @ store
pH 7.6
TA 100
CH 380

 

[PoolStored]

Without knowing TDS, you are a bit of a Crud shoot.

Every 1000 ppm of salt is worth about 6F in temperature difference.

You likely are around 1000 TDS, maybe higher.

Given the crapshoot, choose one and stick with it until done.

 

[wireform]

I like to bring the pool water up a good few degrees to get a solid separation for the delta T so then I know as long as the exchange takes it'll have the best possible outcome.

 

[pizaul]

I like to bring the pool water up a good few degrees to get a solid separation for the delta T so then I know as long as the exchange takes it'll have the best possible outcome.

Hmm do you aim for the difference to be 20F or more? Unfortunately my heater doesn’t work and I don’t have a solar cover. I’d have to wait deeper into the height of summer here in MD for pool temp to creep into low 80s.

Without knowing TDS, you are a bit of a Crud shoot.

Every 1000 ppm of salt is worth about 6F in temperature difference.

You likely are around 1000 TDS, maybe higher.

Given the crapshoot, choose one and stick with it until done.

Yeah I may just have to go with it. In the end it’s helping more than harming anything, and water is cheap.

 

[dBsooner]

Other than the issue of the plaster possibly drying out (I think as long as you go fast enough, it shouldn’t matter?) or the pool “maybe” popping out of the ground if your water table is high… have you though about just doing a drain and replace?

 

[pizaul]

Other than the issue of the plaster possibly drying out (I think as long as you go fast enough, it shouldn’t matter?) or the pool “maybe” popping out of the ground if your water table is high… have you though about just doing a drain and replace?

I have thought about it, but I don’t want to risk those possibilities if I don’t have to lol, which is why the exchange technique triggered my interest and is my preference. I am limited to filling with one garden hose pumping out 6-7GPM. I did also think to just do a few partial drains to skimmer line and fill, however that’s just more time in the end. The exchange route just seems most logical to me if I can figure out best pump and fill arrangement.

 

[wireform]

You can check your munisipality if there is a possibility of filling say through the fire department for a small fee when they need to exchange the water in their tankers. You'd want a quick fill if possible.

 

[pizaul]

Without knowing TDS, you are a bit of a Crud shoot.

Every 1000 ppm of salt is worth about 6F in temperature difference.

You likely are around 1000 TDS, maybe higher.

Given the crapshoot, choose one and stick with it until done.

Got the TDS for my pool water, it’s 600. But without knowing fill water guess that doesn’t help much. Maybe I’ll take a bottle of fill water to pool store and see it’s makeup, but from what I read EPA sets the suggested maximum for tap water to not exceed 500 TDS to be safe for drinking. So it ought to be less than that I’d imagine being county water.

You can check your munisipality if there is a possibility of filling say through the fire department for a small fee when they need to exchange the water in their tankers. You'd want a quick fill if possible.

Hmm, I can check! But for simplicity sake I think I’ll just do small partial drains and fills that don’t expose plaster if I can’t figure out how to do a proper exchange.

 

[PoolStored]

Use TDS of 500 for your fill. Most municipal water sources shoot for that or a bit less.

So (74 - 600/165)- (68 - 500/165) = (74-3.6) - (68-7.7) = 70.4 - 60.3 = 10.1

Fill at bottom of the deep, extract from the top.

 

[pizaul]

Use TDS of 500 for your fill. Most municipal water sources shoot for that or a bit less.

So (74 - 600/165)- (68 - 500/165) = (74-3.6) - (68-7.7) = 70.4 - 60.3 = 10.1

Fill at bottom of the deep, extract from the top.

For the second part wouldn't it be 68-3.03? Making it 70.4 - 64.97 = 5.43? Which puts it nearly at 5 meaning there will be lots of mixing?

Pool temp is 71 this morning so just to have the numbers current:

(71- 600/165) - (68 - 500/165) =
(71 - 3.6) - (68 - 3.03) =
67.4 - 64.97 = 2.43

So with a DeltaT of 2.43 that pretty much guarantees lots of mixing and maybe an exchange is not the most efficient route?

 

[PoolStored]

So with a DeltaT of 2.43 that pretty much guarantees lots of mixing and maybe an exchange is not the most efficient route?

Yea, good catch on the math. No coffee yet.

No, does not guarantee lots of mixing, the water temp difference if you turn pump off likely be enough to minimize mixing.

Fill the deep and take from the top. My delta T was a little bigger, but it came our spot on when I counted the gallons...very little mixing. Exchange is the most efficient and safe route.

 

[pizaul]

Yea, good catch on the math. No coffee yet.

No, does not guarantee lots of mixing, the water temp difference if you turn pump off likely be enough to minimize mixing.

Fill the deep and take from the top. My delta T was a little bigger, but it came our spot on when I counted the gallons...very little mixing. Exchange is the most efficient and safe route.

Haha, i'm on my third cup so VERY awake lol. Glad to have confirmation! For fun I ended up going full YOLO and just doing it this way last night, so 4,320 gallons should have been exchanged by now. Water looks extra brilliant this morning! I'll keep it going for the rest of the day to exchange 11-12k and then do the CYA test tomorrow after pump runs for an hour.

 

[PoolStored]

CYA test tomorrow after pump runs for an hour.

Do you have a dolphin/robot? Throw it in when exchange is done. CYA is funny. So is salt. They take a while to mix...you may find that you don't get a good read for 24-48 hours of mixing...

 

[pizaul]

Do you have a dolphin/robot? Throw it in when exchange is done. CYA is funny. So is salt. They take a while to mix...you may find that you don't get a good read for 24-48 hours of mixing...

I have an aiper seagull pro, i'll do that! We're supposed to get some rain tomorrow so will need to suck up all the worms that enjoy falling to their death to bottom of the pool anyway lol

 

[pizaul]

Exchange complete! Whew. If I measured flows right, I should have exchanged ~15k gallons or so. The water has always looked good, but now it looks next level good. I suppose we call this TFP good, lol. Before heading to work I started the pump up, added some LC, and let the robot do its thing. Will check CYA tomorrow or Sunday to see where its at. This whole process was extremely painless, so much better than waiting hours to drain a few inches, then adding water and waiting hours, and babysitting levels. I'll keep exchanging until I get to 50 CYA or if its close enough let it naturally drop from splash out + fills and rain dilution.

 

[pizaul]

Tested this morning. Proud to report we have gone from 160 CYA to 80! Although a bit high still for non salt, so I’ll do one more exchange to get that down a bit more. I’d def recommend this method to anyone trying to get their CYA down. It’s set and forget once you equalize the flows. And my thirsty trees got some water during this drought here in MD!

 

[dBsooner]

Great news! Science! Good job!!