SWG Acid Washing

[Florida Penguin]

It seems I need to acid wash my SWG every 2-3 months. (FC produciton drops and the cell spends a lot of time in "reverse" mode {as per the LED's on the control panel}). The cell doesnt' look like it has scale, but it improves its function after acid clean.

I also have to keep the SWG up to 50-60% most of the time to keep my FC in the AM 3 or more. I get about a 1.5 to 2.0 FC drop overnight.

I suspected a low grade alge issue, and I shocked the pool with bleach up to a FC of about 15, but it did not make any difference....I still get a 1.5 ppm FC drop overnight.

Numbers:
FC 3-5 range, CH=350, TA=70, CYA=80, pH 7.6-8.0 range...see signature for equipment...I keep the pool heated to 88 F during the day, and with the cover, it stays in the low 80s at night.

My questions are:

1) When doing the acid wash of the SWG (with the dilute acid), how long do you let the cell sit in the acid bath...the instructions say no more than 30 min. But is all the work of the acid done in 5 to 10 min?

2) I suspect my pH probably hits 8 at times, so I may be scaling the SWG a bit more than I should. I have boric acid in the pool to about 50ppm, but even with this the pH rises quickly. I usually add acid 2 times a week.

3) My pool builder is a pretty reputable guy in town, and has been using this SWG for their pools often. His story is that it is hot and sunny in florida, and with keeping the pool warm, there are just a lot of alge to keep at bay. It is his experience that this SWG need to run at 60-80%, even more at times, to keep the FC up.

any thoughts on the above?

 

[JasonLion]

You normally soak in acid for as long as the plates are actively bubbling/foaming up. How long that is depends on how scaled they are. Too much total time in acid can damage the plates, especially if they are not bubbling.

Cell run time depends on the relative size of your SWG and pool, in addition to the usual factors like water temperature, CYA level, and bather load, so it is impossible to directly compare percentages.

You might try letting your TA go down a little more, perhaps to 50 or 60, to slow the PH rise.

 

[Strannik]

You normally soak in acid for as long as the plates are actively bubbling/foaming up.

The fact that it stopped bubbling might also mean that all the acid has been neutralized.

But in general with mild scaling it would mean the cell is clean. Shouldn't take more than 5-10 mins. How strong is your acid? 33%, or are you diluting it?

 

[Florida Penguin]

Type of acid

I am using the formula from the owners manual.

Muriatic acid (standard 30ish%) at about 4 cups per gallon of tap water.

That's the thing....the plates don't really foam, but the SWG starts to work again after the cleaning.

I think I may just do a short clean every 2 months, as that is about the interval where I notice a drop off in FC production.

 

[Strannik]

Interesting. Can you visually see any buildup on plates? How thick is it?
And how old is your SWG?

 

[Florida Penguin]

details...

The SWG is 4 months old.

I do not see any buildup on the plates.

There have been other threads on this SWG with a similar issue. They seem to need a high output time (%) to get the FC to stay up (in warm climates).

Thanks for the interest.

 

[dschlic1]

I know your issue, I am battling a similiar one. To find a rough estimate of you SWCG setting, I recommend:
1. Shock to at least 25 to 30 ppm for at least 3 days or until drop over night is very low. This doesn't kill the beast, but drives it into submission for a while.

2. Let the chlorine level drop. When at about ten, measure the drop over a period of 24 hours. This is your appromixate chlorine demand.

3. Using the above number, and the rated chlorine production of your cell, calculate how many minutes per day, the cell needs to be on. Then using your current filter run time, find how many cycles will occur daily. Divide the minutes by the number of cycles, this gives the number of minutes per cycle. Divide the minutes per cycle by the cycle time, and this is your approx setting.

BTW try turning on your cell when the chlorine just drops below 10 ppm at the above setting and see how it works. For me this works for a while, but then the "beast" comes back.

 

[Strannik]

That's exactly why i'm strongly against rating SWGs on a gallon basis, because it may vary dramatically depending on a number of variables.

 

[Florida Penguin]

Hmmm

I have been watching my overnight drop in FC for the past week. It has been a consitent 2 ppm drop overnight.

I understand your above procedure.

So it sounds like the 2 ppm drop is too much to be a "normal" drop, and it probaly does indicate an excessive smoldering alge issue.

Did I get this right?

 

[JasonLion]

Yes, if you are losing more than 0.5 of FC overnight then you have something growing in the pool.

 

[Florida Penguin]

OK....

I will let things stay as they are thru the weekend, then I will do the "super shock" for a few days as descibed above next week.

I may need some help with the calculations. But I will get the data from my pool first and then I can get help crunching the numbers later.

Thanks!

 

[dschlic1]

A further note. Last week my FC level dropped below 7 which again started an small infestation. My chlorine demand went from 1.3 ppm to over 2 ppm per day even though I brought the chlorine level back up to over 9 ppm. I didn't really want to shock the pool again, so I tried some quat based algaecide at a reduced dosage. That seemed to do the trick, and my chlorine demand is back down below 1.5 ppm. I know many people on this forum are opposed to algaecide, but in this case it appears to be an alternative.

 

[Poolsean]

Other things to consider on question #3...

Dogs - if you have dogs and they jump in the pool, it's as though you have 5 kids jumping in the pool. HEAVY consumption of chlorine.
Organics (leaves, branches, fertilizer) - will leave phosphates in the water and if it gets high, can create a chlorine consumption. Can encourage sustaining algae growth.

You didn't mention that you're having a hard time generating enough chlorine. Is the system ok on this part?
It seems like you're losing chlorine overnight at a rapid rate, and after acid washing, this is reduced to a normal chlorine loss?

 

[Florida Penguin]

Answers-

1) No dogs or other animals in pool
2) No leaves, etc (we have a screening in lanai)
3) The SWG seems to be working....I can get the FC level up 4-6 points if I crank it up to 80% for the 10-12 hr run time, and that is during the day as well.

I am now in the middle of my 2-3 day supershock now...with FC levels 25-30 (and CYA about 70) and constant pump running.

I will post results later this week when I am back to normal pump/SWG operations.

 

[dschlic1]

A couple of ideas:
A note to the admins, you might want to start a new thread with some of these posts as they have changed subjects.
Excuse me if I am stating the obivious, but Florida Penguin make sure that you have all piping open and water circulating through all piping, equipment etc during the shock process.
Also when did you last check your CYA levels? In my case I have had sudden drops in CYA levels. However I recommend that you do not ad any CYA.

 

[Florida Penguin]

Continued Answers-

1) All pumps are on (both filter pump and spa jet pump)
2) Waterfall (pool return ) is on.....thus water is flowing in all pipes, etc.
3) Automatic pool cleaner is always on a little bit, so there there is flow thru that pipe as well.
4) I checked CYA level last week with TF-100 kit....level was 70. Also confirmed by my local pool store, as I have to bring in my water to a "professional tester" once a month for the first year of operation for my pool warranty to be valid.

So far, it has been real easy keeping the FC level at about 30.....and I did not detect more than 0.5 to 1.0 drop overnight in FC (although at that high level, I am not sure how accurate the TF-100 test kit isf for such a small change.)

One more day of full dose shock (FC=30), and then I will let it drop back down.

 

[Florida Penguin]

:-D Well, it has been a week. My FC levels are slowly drifting down. My FC was now down to 16 this AM. No change overnight as well. So it seems to be true....I probably did have a low-grade smoldering alge problem that was using up my FC overnight.

Also, I am kinda surprised how long the FC lasts. It has been over a week and it has taken this long for my FC to go from 30 to 16. (With no other FC input, SWG off, etc.). My CYA level is 80. I seem to lose about 3 ppm a day in FC levels.

Also, this experiement makes me wonder why we keep the FC levels so low. I went swimming in the pool a bunch over the past few days. I did not notice any problems with the FC being this high. Maybe over time it will affect bathing suits, but for a few hours, it doesn't seem to matter.

I think I will keep my FC levels no lower than 5 to 6 ppm. Why push the envelope and allow the FC levels get below 3 or 4 and risk an alge problem?

 

[dschlic1]

I have to maintain FC level above 8. It has been my experience that if the FC goes below 8, even for less than a day, my chlorine demand rises. It is a real PITA because I have to run at chlroine levels that are above the ranges of the simple tests. (OTO for example). Also I have a small pool, and if I have a pool party and forget to super chlorinate during that party, bingo I have a problem. Another issue is that even though the demand rise is small, the only way to eliminate is to shock to very high levels.

 

[JasonLion]

With a SWG and CYA of 80 many people find that they can run with their FC level around 4. If you consistently need much higher levels than that it is possible that you have some algae growth in a hidden spot, often a light niche, that does not get completely killed off by shocking. If you can find that spot and clean it out you can often lower your FC level and not have problems. It is also believed, but not really proven, that extremely high phosphate levels can require somewhat higher FC levels to reliably stop algae.

 

[Florida Penguin]

It seems there are two issues here

1) I will plan on keeping the FC in the 5 to 6 range and I will update this thread in a few weeks with the results of how it is going.

2) It sounds like JasonLion was responding to both my issue and dschlic1's issues. From my perspective, I feel pretty confident I got all the areas that could have alge during my 3 days of supershock (FC>=30). There was a small area (< 3 sq inches) on the pool cover that had some alge on it, but that is a non-isssue at this time since I put the cover away for the summer.

3) I check my phos levels as well, and the last one was 300 or 400 (not very high).

4) I kinda like using liquid chlorine (Bleach) directly. I think when my SWG eventually goes, I will look into the cost of switching to straight-up bleach or liq chlorine dispenser. It just "feels" better...knowing that you are adding exactly what you need, when you need it. I find that you are never really sure what the SWG is up to (ie- working good or not on any particular day).

Thanks for the input!