Jandy Aquapure PLC1400 SWCG scale build up after a few weeks, only on the output "grate"

[TaylorN]

Hey there.

Curious as to why I keep getting scale build up on the output "grate" side of my Jandy Aquapure PLC1400 cell after only about 2-3 weeks of running. It doesn't seem to build up on the face of the plates themselves but rather just the end-grate that holds the plates in place. Same thing was occurring on my old SWCG before it died after 4 years. I am able to use a plastic utensil to break off the scale relatively easy, without needing any acid, but if it goes too long I'd imagine it will start impeding flow.

I will get some proper CSI numbers next week, but the last time I measured, these were what I remember (any number without a "~" prefix is up to date and accurate):
water temp: 90. Technically the vast majority of the water is 87 degrees, but when running most of the day at 1600rpm with the pool cover closed, most of the water that goes through the pump is from the top layer and that combination of water is 90 degrees.
pH: ~7.4-7.8
TA: ??
Calcium hardness: ~350-500
salt: ~3600
fC: 5 (SWCG is set to 60%, which keeps the fC level stable, but currently fC=5 is probably a little high and needs to be more like fC=3)
CYA: ~80-90
Borate: 0
TDS: ? (water was complete refill 4.5 years ago)

I run the pump at 1600rpm (1200rpm will have low flow error) from 6am to 5pm, with the exception being a 1hr run from 12pm-1pm @2850rpm and a 30min run from 4:30-5pm@2850. Well, the solar heater might kick on for a couple hours in the morning at 2200rpm, but by noon the pool is at above set temperature. Oh, and the SWCG is plumbed in a vertical configuration so the output is at the top, then the piping does a u-turn and goes back to the ground and then the piping goes back vertical a foot to the return valve before going back down underground (I can share a photo if necessary)

I am curious why the SWCG output grate is seeing the build up. Could it be the positive CSI? But why would it not be on the input grate or the cell plate faces themselves? If it is the positive CSI, how would I get it to be slightly negative without a refill of the pool, especially since my tap water is probably 250-350 calcium down here in San Diego, CA. I am afraid even a partial refill won't help significantly. I supposed I could add acid (to reduce the pH) twice a week instead of 1 a week, to keep the pH and TA consistently on the lower end of the range (though I might be talking out of my Rear with that).

Anyways. I am including a before and after cleaning of the SWCG. Is there any other information I am leaving out?

Thanks!

 

[PoolGate]

I question your test numbers. Can you share your PoolMath with the forum? Scale buildup occurs when CSI is too high. I get 0 scale buildup on my cell and in 6 seasons have never had any at all. Can you be more specific on your CH level? How old are your reagents?

 

[TaylorN]

Yeah, I question them too I will get better numbers this weekend or next week.

 

[TaylorN]

Note, my pool is 23.5k gallons (corrected in signature)

Tested with two different Taylor Kits...
pH: 7.6 (normally targeted 7.4 with muriatic acid)
TA: 110
Calcium hardness: min:500 max:550
salt: min 2950 (with digital salt meter)
fC: 4.5
CYA: ~80
Borate: 0
TDS: ~4000 (taken with digital meter)

Does the orientation of the SWCG at all matter (see attached images for my-installation vs pentair-recommended vs jandy-recommended)? I can't see why that would be the case unless at lower flow (1400rpm) the hydrogen bubbles are bubbling up from the plates and causing some weird chemistry/fluid-dynamics at the top of the plate where the electrodes connect which causes extra scaling.

 

[TaylorN]

...Pentair recommends a minimum 25(+/-)gpm while Jandy recommends 30gpm flow. Maybe 1400rpm is not enough flow to hit 25-30gpm? I'd venture it is pretty close especially since I don't get a low flow sensor error from the aquapure unit until about 1200rpm

 

[generessler]

Hi. Obviously the cell is in none of the recommended Jandy orientations. I don't know if that's okay, but using a Pentaire manual for a different Jandy cell isn't a recipe for success. Mine is in position A with no issues. Similar water numbers.

Check the SWG tab of the chlorine chart. FC target is 6, minimum of 4 at CYA 80.

I'm not seeing a check valve between SWG and heater. There's supposed to be one to protect the copper heat exchanger, a pricey item.

 

[JamesW]

What is your CSI?

Turn on CSI tracking.

Are you using the heater?

If yes, the temperature at the output is about 17 degrees hotter at 40 GPM, which will increase the CSI.

 

[JamesW]

https://www.pentair.com/content/dam/extranet/nam/pentair-pool/residential/manuals/heaters/mastertemp/Manual-MasterTemp-472592-English.pdf

 

[JamesW]

TDS: ~4000 (taken with digital meter)

Don't use the TDS setting on your meter; it does not work correctly for a salt pool.

Only use the salinity setting.

Does the orientation of the SWCG at all matter

There are directional arrows, but it work in either direction.

Pentair recommends a minimum 25(+/-)gpm

Pentair recommends 40 GPM minimum for the MT400.

Lower the CSI to the -0.3 to 0.0 range.

Try to make sure that you are getting at least 40 GPM.

 

[TaylorN]

@JamesW, I turned on CSI tracking in the Pool Math app from TFP, though I don't see where that get stored/logged. I can click on the CSI tab with the rest of the variables (ph/CH/etc) and it always asks for temp/salt/borates. I type in temp:87/salt:2950/borates:0 and it returns a CSI of 0.18.

If I manually perform the calculation from the Pentair manual, I also get 0.19

We don't use the gas heater for the pool, but we occasionally use it for the spa. However, we do run the solar heater every day for a couple hours. Since the solar return enters before the SWCG input, would it makes since to replumb it so the solar return enters AFTER the SWCG? that would cut down on the really high heat from the solar panels entering the SWCG, and thus the CSI which might be 0.37+ at 110+ degrees would be back down to 0.19 during solar heating. That is an interesting thought!

So maybe I can work (hard) to reduce the Akalinity by -20 to say 90 (if lucky), add some salt to get up to 3600, double check the CYA is at ~80, and ponder if the solar heater should be plumbed in behind the SWCG.

What is your CSI?

Turn on CSI tracking.

Are you using the heater?

If yes, the temperature at the output is about 17 degrees hotter at 40 GPM, which will increase the CSI.

View attachment 442743View attachment 442744

 

[TaylorN]

I was using a digital pen type reader for the salinity and TDS, not the Jandy sensor built into the Aquapure.

Someone gave me a FlowVis gpm flow meter, that I should install at some point so I can get an accurate GPM and dial in the RPM better. I was always following the recommendations on the forums to stay at as low of RPM as I could to save electricity....

Don't use the TDS setting on your meter; it does not work correctly for a salt pool.

Only use the salinity setting.

There are directional arrows, but it work in either direction.

Pentair recommends 40 GPM minimum for the MT400.

Lower the CSI to the -0.3 to 0.0 range.

Try to make sure that you are getting at least 40 GPM.

 

[JamesW]

Since the solar return enters before the SWCG input, would it makes since to replumb it so the solar return enters AFTER the SWCG?

Maybe just increase the flow some.

 

[TaylorN]

Hi. Obviously the cell is in none of the recommended Jandy orientations. I don't know if that's okay, but using a Pentaire manual for a different Jandy cell isn't a recipe for success. Mine is in position A with no issues. Similar water numbers.

Check the SWG tab of the chlorine chart. FC target is 6, minimum of 4 at CYA 80.

I'm not seeing a check valve between SWG and heater. There's supposed to be one to protect the copper heat exchanger, a pricey item.

@generessler , thanks for looking out on multiple fronts!

Can you include a photo of your setup? I just want to have a reference.

I just happened to have re-read that SWG tab of the chlorine chart this afternoon and will try to get the FC up to 6 with CYA at 80, but fC doesn't affect CSI, right (just making sure I am not misreading things)?

I don't have a check valve between the SWCG and the heater as I was figuring only a minimal amount of higher chlorinated water might flow back into the heater when the pumps turn off. Any unabsorbed chlorine gas or hydrogen should rise up into that vertical u-turn(?) Guess it couldn't hurt to plumb in a check valve right after the heater though.

 

[wireform]

I don't have a check valve between the SWCG and the heater as I was figuring only a minimal amount of higher chlorinated water might flow back into the heater when the pumps turn off. Any unabsorbed chlorine gas or hydrogen should rise up into that vertical u-turn(?) Guess it couldn't hurt to plumb in a check valve right after the heater though.

You don't need one that's for chlorinators now SWCG's

 

[TaylorN]

I meant to say maybe I should plumb the solar panels to receive input from the plumbing after the SWCG.

But I guess I could increase the flow during solar heating (currently: 2200rpm, could be max:2850), which would be beneficial to localized SWCG's CSI

Maybe just increase the flow some.

 

[TaylorN]

You don't need one that's for chlorinators now SWCG's

Thanks for the feedback!

 

[generessler]

Thanks for the feedback!

You don't need one that's for chlorinators now SWCG's

Well I guess it's a matter of opinion. The AquaPure manual shows them in recommended plumbing diagrams (Figures 4 and 5 in my copy). Inyo says yes with either swg or feeder. Swimming Pool Steve says strong yes and claims in 30+ years of servicing pools he's seen many heaters die early for the lack. The MasterTemp manual just says "chlorinator" without being too specific.

 

[wireform]

The concensus here on TFP has been skip it with SWCG because unless the cell is energized it's it's a lame duck and would need to be powered without water flow and that's highly unlikely cuz it has been stressed over and over not to rely solely on the flow switch but to have 2 safeties the second being a time clock or wired with the pump.

 

[TaylorN]

The concensus here on TFP has been skip it with SWCG because unless the cell is energized it's it's a lame duck and would need to be powered without water flow and that's highly unlikely cuz it has been stressed over and over not to rely solely on the flow switch but to have 2 safeties the second being a time clock or wired with the pump.

Thanks @wireform

 

[TaylorN]

I installed the FlowVis Flowmeter and at 1400rpm the pump is only running at 7-8gpm. The Jandy manual for the SWCG says to run a minimum of 20gpm. However the low flow sensor doesn't come on until 1200rpm and everything I have read on the forum about RPM for SWCG is that you should go as low as you can until you get the low flow light to turn on and then increase the RPM by 100-200rpm, hence using as little electricity as possible. That is how I ended up at 1400rpm. It seemed to produce enough chlorine, but I am obviously now trying to analyze all the variables since the cell is scaling quite quickly (not on the plates, but the electrodes/grate), even though the saturation index is not terribly out of whack. Going to use a calibrated salt/tds sensor tomorrow to get a more accurate reading of that.

here is the following GPM breakdown at various RPMs.

NO SOLAR heating
Pool:
1400rpm=7-8gpm
1600rpm=10gpm
1800rpm=11-12gpm
1900rpm=14-15gpm
2000rpm=19gpm
2050rpm=20gpm
2200rpm=23-24gpm
2850rpm("high" speed)=39-40gpm

Spa mode:
1400rpm=7-8gpm
2050rpm=20gpm
2150rpm=21gpm

Spillover:
3100rpm= 42-43gpm

WITH SOLAR heating (half of the array is on 1st story, half on 2nd story)
Pool:
2200rpm=19gpm
2300rpm=20gpm

Note, I thought it would have taken a lot more RPM to push water up to second story vs not having solar turned on. Looks like only a difference of ~200rpm to get to 20gpm