Dealing with scaling in SWG

[dailo]

Not sure why but this season my SWG has been scaling very quickly. I assume its due to my CSI tending positive quickly because my CH is high and my fill water is hard. This was my plan to try to slow it down, but not sure what the best/cheapest way to do it.

- Keep PH at 7.2 to keep CSI negative, but going to burn through a lot of acid.
- Read other threads that using borates could help lower PH inside the cell. Going to get test strips to see where it is now and add some to bring it up to 30ppm or so
- Start filling with soft water to try to lower CH over time as I don’t want to pump out water to lower CH

FC - 5.5
CYA - 50
PH - 7.5
TA - 110 (use so much acid and doesn’t go down much, was 130)
CH - 425
Cell Temp - Between 80 to 90F

 

[JamesW]

Are you using a heater?

High temperatures after a heater increase the CSI.

Monitor the cell temperature as the heater comes on to see how high the cell water temperature is getting.

 

[ajw22]

Lower TA to 60-70.

Lower Total Alkalinity

A lower Total Alkalinity level can help a pool owner stabalize their pH increase. We'll explain how to lower TA with a little help from muriatic acid.

www.troublefreepool.com

Your water will have no borates if you have not added any. If you add borates add 50ppm.

Borates in pool - Further Reading

www.troublefreepool.com

 

[dailo]

Lower TA to 60-70.

Lower Total Alkalinity

A lower Total Alkalinity level can help a pool owner stabalize their pH increase. We'll explain how to lower TA with a little help from muriatic acid.

www.troublefreepool.com

Your water will have no borates if you have not added any. If you add borates add 50ppm.

Borates in pool - Further Reading

www.troublefreepool.com

Thanks. I am not sure if previous owner put any borates, I think they may have as I didn’t have any issues when I first took over the house as all the other measurements are consistent with previous years.

I’ve tried to lower TA but it seems to always creep back up. Should TA lower with every acid pour? Ive brought pH down from ~7.6 to 7.2 a few times now and TA has only dropped down a little but like from 120 to 110.

 

[dailo]

Are you using a heater?

High temperatures after a heater increase the CSI.

Monitor the cell temperature as the heater comes on to see how high the cell water temperature is getting.

I have a solar heater and I think highest is temps get to maybe 95. As long as I keep pH around 7.2 it seems to be okay, but hard to keep it there for long.

 

[JamesW]

You probably need to lower the TA.

Keep adding acid to lower the pH to 7.2 and the TA will come down but you have to be consistent.

Adding borates might help.

 

[ajw22]

I’ve tried to lower TA but it seems to always creep back up. Should TA lower with every acid pour?

Yes. Use
PoolMath Effects of Adding to see how much.

Ive brought pH down from ~7.6 to 7.2 a few times now and TA has only dropped down a little but like from 120 to 110.

What is the pH and TA of your fill water?

 

[dailo]

Yes. Use
PoolMath Effects of Adding to see how much.


What is the pH and TA of your fill water?

Good point, didn’t think about testing that since I don’t have to refill that often.

 

[SoCalTFP]

With the summer evaporation your fill water is probably high in TA. The only way to bring it down is more MA additions, so target a lower PH and be liberal with a spillway if you have it for aeration.

Borates might help. Some of the subjective water feel and look stuff might be worth it. Use Boric Acid it’s an easier addition.

Your CH is pretty good though so you could be worried about nothing though.

 

[dailo]

With the summer evaporation your fill water is probably high in TA. The only way to bring it down is more MA additions, so target a lower PH and be liberal with a spillway if you have it for aeration.

Borates might help. Some of the subjective water feel and look stuff might be worth it. Use Boric Acid it’s an easier addition.

Your CH is pretty good though so you could be worried about nothing though.

I thought target for CH is lower? Good to know through. I’m spending so much on MA this year

 

[SoCalTFP]

I thought target for CH is lower? Good to know through. I’m spending so much on MA this year

My SWG ideal is 350-550 per pool math. I’m currently at 700+ so managing CSI is more of a chore. I’m surprised your having SWG scaling issues at 425.

Borates could help. I’ve read a few things about them buffering PH rise inside the SWG because that can spike higher than the overall water. I’d imagine that would impact CSI within the cell itself. Boric Acid isn’t cheap but you shouldn’t need to add it frequently.

 

[jesse-99]

Are you using a heater?

High temperatures after a heater increase the CSI.

Monitor the cell temperature as the heater comes on to see how high the cell water temperature is getting.

I never considered that the CSI inside a cell may be more positive than in the pool, since temp does figure into CSI it makes sense. Any idea how much hotter the water typically is coming straight out of a heater? If for example the heater temp is set for 85, and the inlet water temp is 80, what would the outlet water temp typically be? 85? 95? Just curious.

 

[ajw22]

I never considered that the CSI inside a cell may be more positive than in the pool, since temp does figure into CSI it makes sense. Any idea how much hotter the water typically is coming straight out of a heater? If for example the heater temp is set for 85, and the inlet water temp is 80, what would the outlet water temp typically be? 85? 95? Just curious.

8 to 16F temperature rise. Heater outlet temperature rise will depend on the water flow rate. Slower water flow will have greater outlet temperature since the same BTUs go into less water volume.

Read Heater Maintenance - Further Reading

 

[jesse-99]

8 to 16F temperature rise. Heater outlet temperature rise will depend on the water flow rate. Slower water flow will have greater outlet temperature since the same BTUs go into less water volume.

Read Heater Maintenance - Further Reading

Very helpful, thanks. So the impact on CSI inside a post-heater SWG (relating to the scale conversation above) is pretty minor overall based on that. I didn't know if the water was 8 degrees higher or 50 degrees higher.

 

[JamesW]

If for example the heater temp is set for 85, and the inlet water temp is 80, what would the outlet water temp typically be?

A 400,000 btu/hr heater with 40 gpm flow has a temperature rise of about 16.8 degrees.

So, 80 inlet is 96.8 outlet.

 

[JamesW]

If you have a hot tub, the heater outlet temperature can get up to 120.8 degrees.

104 + 16.8 = 120.8.

For example, a 400,000 btu/hr heater with an efficiency of 84% transfers 336,000 btu per hour to the water.[4]

At a minimum required flow of 40 gpm, there will be 2,400 gallons of water (20,000 lbs.) that receives the heat.

Each btu raises the temperature of one pound of water by one degree Fahrenheit.

336,000 btu into 20,000 pounds of water is 16.8 degrees of temperature rise (336,000/20,000).

So, the maximum temperature rise you should ever have is 16.8 degrees Fahrenheit.

As shown below, higher flow results in a lower temperature rise.

40 gpm = 16.8 degrees temperature rise

50 gpm = 13.44 degrees temperature rise

60 gpm = 11.2 degrees temperature rise

70 gpm = 9.6 degrees.

80 gpm = 8.4 degrees.

Heater Maintenance - Further Reading

www.troublefreepool.com

 

[dailo]

Just took a new set of tests this morning:

Pool:
TA: 120
CH: 450
pH: 7.4
FC: 4 (looks like scaling is happening already happening and need to bump up the %)

Fill Water:
TA: 240
CH: 125 (guess CH isn't the problem after all, thought it would be much higher)
pH: 8.0

Getting my borate test strips later today, so will will get that and see how much boric acid I'll need. I guess with the TA of my fill water so high, just going to have to constantly battle keeping pH lower. With it being so hot lately I haven't needed to turn on the solar heater, but will keep an eye on the cell temp. I have an Hayward T-15 Cell paired with a Aqalgoic controller that reports what the cell temp is, but not sure how accurate it is.

 

[JamesW]

Granular Boric Acid, 55 lb [boric55] | DudaDiesel Biodiesel Supplies

You need to keep the pH down at about 7.2 until the TA comes down.

With your high fill TA, it is going to be a constant battle.

 

[dailo]

Granular Boric Acid, 55 lb [boric55] | DudaDiesel Biodiesel Supplies

You need to keep the pH down at about 7.2 until the TA comes down.

With your high fill TA, it is going to be a constant battle.

Going to see if I can buy MA in bulk or something, going to need a lot! Thank you all for the help!

 

[wireform]

Maybe an RV water softener set up like some here have just for the autofill/or fill water can help the situation. Not sure what or if it helps with TA.