Will high Ca Level Reduce SWG Output?

[BassTrix]

I'm on my 2nd season as a pool owner and having difficulty maintaining adequate FC levels this season.

This season I'm having to run 11 hrs total on SWG to equal FC levels achieved last season with 8hrs total run time (4 day/4 night). I maintain chemistry per TFP guidelines for SWG.

Current measures are as follows:

FC 6.0 (7 AM)
CC barely above zero
pH 7.6 (maintain @ 7.5-7.8)
TA 65 (maintained @ 60-70)
CH 600
CYA 75
Salt 5400 (this wasn't intentional, but SWG Mfg says up to 6000 is OK)
Temp: 85-90 depending on time of day.

This spring I replaced the salt cell with an aftermarket. I increased the CYA from 60 to 75 and CH was running from 200-350 over the course of the summer. I'm inspecting and cleaning the cell weekly and finding flakes of Ca in the sock from floor drain. The cell isn't clogged by any means, but it will always have some deposits.

I've measured FC directly from a return and consistently get 1ppm > than a sample from the pool.

My questions are:

1. Will an increase in CH reduce the efficiency of SWG?
2. Is the pH range I'm maintaining appropriate or should I try to run it a bit lower?
3. Does the FC level directly from return (1ppm > pool) sound about right? I can provide pump info if needed.

Thanks in advance for your input.
BT

 

[jblizzle]

1. Yes, if there is scaling in the cell
2. With the high CH,, you should let the pH more.
3. Seems reasonable. Not sure there is a norm.

 

[BassTrix]

1. Yes, if there is scaling in the cell
2. With the high CH,, you should let the pH more.
3. Seems reasonable. Not sure there is a norm.

Hi, I'm not clear on your response to #2. Assuming you meant to say "lower the pH more", how much more do you recommend?

One other question I forgot to add:

What could be the cause for 38% increase in pump time to maintain last season's FC levels and should I be concerned?

Thanks,
BT

 

[jblizzle]

Should have been lower, not let. ... Autocorrect

Check the CSI in PoolMath, you want it slightly negative for a SWG pool.

Lower CYA, more sun, calcium build up, cell degradation from too many acid cleanings ... All could make the FC level lower than expected.

 

[BassTrix]

I generally let CSI drift up to 0 or slightly positive and target -.3 when I adjust pH. The pH at CSI of -.3 is right at 7.5. Do you recommend any changes to what I'm doing?

 

[ping]

How long does the pH stay at 7.5?

Is the SWG building up scale?

With SWG pools it is best to keep the CSI a little negative, I try to keep it between -.3/-.1.

 

[BassTrix]

How long does the pH stay at 7.5?

A very short time. On the occasions when I have added acid and rechecked, it seems to remain at 7.5 for about an hour or two of SWG run time. It takes 2 days to drift from 7.5 up to 7.8.

Is the SWG building up scale?

Yes and I'm finding flakes in the floor skimmer sock...I presume this is flaking off the SWG when it reverses polarity. I've been cleaning it weekly for the past 3 weeks but before after measures comparing water from a return vs from the pool consistently show 1 ppm higher from the return.

With SWG pools it is best to keep the CSI a little negative, I try to keep it between -.3/-.1.

If I let pH reach 7.8, I end up slightly positive on CSI. Sounds like I need to tighten up the pH control and keep it closer to 7.5?

 

[ping]

You might want to look into adding 50ppm of borates to the pool. It will help slow down the pH rise and help with the CSI in your case.

Keep the pH closer to 7.5 than 7.8.

 

[chem geek]

Also, in particular, the 50 ppm borates cuts down the pH rise in the SWCG cell roughly in half so should significantly reduce the amount of scale buildup in the SWCG cell.

 

[BassTrix]

Also, in particular, the 50 ppm borates cuts down the pH rise in the SWCG cell roughly in half so should significantly reduce the amount of scale buildup in the SWCG cell.

My tentative plan has been to refill next spring and add borates at that time (since my CH is 600 and rising with 200ppm fill water). Your reply indicates I should rethink this and perhaps add the borates now.

I understand that adding borates will help to stabilize the pH. Based on my current chemistry, I'd have to add 3x the amount of acid with 50ppm borates. On average I need to add ~4oz of acid/day.

Can you give me an idea of how acid consumption would change after adding 50ppm borates?

Is there any reason why, other than the time and $, not to add the borates now?

Benefits:
Less frequent pH adjustments
Less frequent SWGC cleaning = less wear on cell plates due to acid erosion
Prettier water

Costs:
$/time to add borates
$ to get borate strips
3x acid needed to raise pH
anything else?

Thanks,
BT

 

[chem geek]

The total amount of acid is the same over time. You just add larger amounts less frequently, but per unit time it's the same. This assumes you don't have swim jets with extraordinary aeration in your pool since for whatever reason adding borates made that pH and TA rise situation worse (and is unexplained).

As for not adding now, no reason other than time and money as you point out. If you have dogs, then while it's still likely safe some people avoid adding borates if their dogs use the pool as a large drinking bowl (see Are Borates Safe to Use?).

 

[BassTrix]

Thanks to everyone for all the helpful input!

 

[BassTrix]

Keeping the pH controlled between 7.5&7.6, I'm measuring an increase in FC of 0.6-0.8 during the overnight cycle of 5 hours. By my turnover calculations, I should be generating more than 2x that amount of FC in that period of time.

Suspecting the SWCG as the culprit, I contacted Compupool Customer Service and was asked to obtain a measure of phosphates in the water and that the level should be below 100ppm. Is there any validity to this recommendation with regard to FC consumption? My CC levels are at or very near zero.

 

[jblizzle]

No there is no validity to that recommendation as the phosphates should not matter if there is no algae to eat it.
Tell them it is below 100ppm and see what their next big idea is.

Looks like the ECS-16 SWG should make 0.84 pounds of chlorine per day.
So in 5 hours (assuming running at 100% output) that would be 0.175 pounds (2.8 oz) which should equate to 1.4ppm FC in your pool.
Looks like you calcs were the same.
But, it is not unreasonable to lose up to 1ppm of FC overnight even if there was nothing trying to actively grow in the water due to low FC levels. Although the loss should be less at the lower FC levels.

Does the SWG have a % output adjustment? Is it at 100%?
Have you Performed the Overnight Chlorine Loss Test to ensure there is nothing in the water?

 

[BassTrix]

Yes, it's running at 100% for a total of 11 hours/day.

Another interesting (to me, anyway) fact is that I start the day cycle at 7 AM. I've checked FC many times right at 7 and then again just before it shuts off at 1 PM and the FC will be the same. I seem to recall that last season, it would increate by .5ppm....but then again, I'm relying on memory

 

[rcy]

This spring I replaced the salt cell with an aftermarket.

BT

Could this be the reason right here? Aftermarket cell that isn't as good as the original, or did you replace with the aftermarket cell because you found the original cell wasn't performing as well as it was last year?

 

[BassTrix]

Could this be the reason right here? Aftermarket cell that isn't as good as the original, or did you replace with the aftermarket cell because you found the original cell wasn't performing as well as it was last year?

Yes, and I have installed the former cell and have been comparing output levels. When I initially installed the new cell, I compared the FC directly from a return and both matched. This was repeated when the old cell was reinstalled and this time, the output of the old cell was .2 ppm higher (which I think is within the error of the test). Overnight generation rate comparisons showed they are both creating about the same amount of Cl. The overnight generation is a very subjective way to compare due to several uncontrollable parameters.

I've since added 50ppm borates and will reinstall the aftermarket cell and repeat the comparison.

Cl generation seems to have improved with the tightly controlled pH. I say "seems" because I don't have as many data points when I was letting the pH drift up to 7.8 instead of bumping it back down every day.

 

[JoyfulNoise]

Just a comment here but I think your salt cell is undersized for your pool. Your cell produces 0.8lbs of chlorine per day. My IC40 produces 1.4lbs/day. My pool is very close in volume to yours (16000 gal). So you're running your cell very hard (100% output) everyday which is definitely going to shorten their life span.

Next time you replace, if the cost isn't prohibitive, you might want to consider a larger cell output. When my cell dies, in definitely going to upgrade to an IC60 (2.0lbs/day).


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[BassTrix]

Just a comment here but I think your salt cell is undersized for your pool. Your cell produces 0.8lbs of chlorine per day. My IC40 produces 1.4lbs/day. My pool is very close in volume to yours (16000 gal). So you're running your cell very hard (100% output) everyday which is definitely going to shorten their life span.

Next time you replace, if the cost isn't prohibitive, you might want to consider a larger cell output. When my cell dies, in definitely going to upgrade to an IC60 (2.0lbs/day).


Sent from my iPhone using Tapatalk

I agree with you on the capacity of my SWG. The literature for this thing states for pools up to 18k gallons...considering my geographical location, I think the builder (or whomever chose the system) should have chosen the next size up. I have no idea how long the power supply or "old" cell were in operation, but it looks like it's been around a while. Looking at the service manual, it appears they are stepping up voltages on some of the circuits for the "24" model. Based on this, it looks like my PS won't support a higher capacity cell. When the PS dies, I'll definitely be choosing something with higher capacity.

...now you have me thinking that I should take a look at the cost of running the pumps x additional hours a day and see if it makes sense to upgrade sooner than later. I'm guessing it'll take several years to make up the difference in cost but worth a look...especially since I have all the data.

 

[JoyfulNoise]

You can certainly trade off cell power with additional pump time to see if that helps. But if you're at > 8hrs and 100%, then you may already be at the optimal point.

PBs and Manufacturers always seem to undersize their SWG specs because they adopt incorrect standards (1-3ppm FC irrespective of CYA). So if you start with incorrect assumptions, then the cell performance will be less than what is needed. TFP always recommends 1.5-2X upsizing the cell with respect to pool volume.


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