Low Ta, High Ph With Swg System

[Scotsman]

I have a 22 gallon pool, SWG system that is keeping the chlorine levels good (just turned down the level setting). I have a high pH and have been adding MA to lower, but it always stays high.

I got a sample tested and the main points were:

FC 4

CC 0

pH 7.9

Alkalinity 75

CA 40

The store said to add 8lb sodium bicarbonate to raise TA, then 1pt, 10oz MA to lower pH. Then some shock and 6.5 lbs stabilizer (to increase CA?).

I've added the sod bicarb and the TA hasn't increased much. I did start adding a little MA to try to get the pH down since I was adding the sod bicarb in stages. I still have to add more MA but my basic question is this - won't adding MA to lower the pH also lower the TA? It seems to me I shouldn't have both together i.e. I don't understand why if my alkalinity is low then how come pH is high? I also read that you add MA to reduce TA?

I do also have a question about activating my in-floor cleaning but thats for another day.

Thanks in advance.

[chem geek]

With an SWG, it outputs hydrogen gas bubbles (you can see them readily at night if you run the pump and SWG and turn on an interior pool light) and that aeration causes carbon dioxide to outgas from the pool and that causes the pH to rise. So ironically, a lower TA is better. Mostly, though, you want to figure out a way to lower your chlorine demand so that you can lower your SWG output. Using an algaecide will help and some people use 30-50 ppm Borates in their pool for that reason -- both as an algaecide and as an additional pH buffer that is not carbonate (so won't outgas). So I wouldn't add any Alkalinity Up.

Some SWG manufacturers recommend 60-80 ppm CYA and if your pool gets a lot of sun then that does seem to cut down the breakdown of chlorine from sunlight quite a bit. If you do this, you should set your FC level to around 4.5% of the CYA level (at least). Most SWG pools do seem to operate OK at these lower chlorine levels, but not all do (manually dosed chlorine pools usually need a minimum FC of 7.5% of the CYA level to keep away green algae). Your 4 ppm FC at 40 ppm CYA is more than you need for an SWG pool. So increasing the CYA could help -- or lowering the FC target to 3 ppm can help as well (if it lets you lower your SWG output time).

Using a pool cover to keep the sun's UV rays off the pool will help -- again, if it lets you lower your SWG output.

Finally, if you do keep a lower TA, then a higher pH of around 7.7 compensates to keep calclium carbonate saturation (if you have a plaster pool) and it will also outgas less at the higher pH.

Since you just lowered your SWG output, why not see if things improve just from that -- and let us know. Also, if CA is Calcium Hardness (also abbreviated as CH), then you must have a vinyl pool, is that right? Otherwise, you would need more calcium. With a vinyl pool, you can easily go to a lower TA (even as low as 50), but see how things go with your recent changes of lowering your SWG output and your lower TA.

Richard

[Scotsman]

Thanks Richard. I don't fully understand the TA levels yet and so your comment about keeping it low is confusing and is different from what the shop was recommending - they said 80-120, knowing I had an SWG.

To be honest, I just started keeping my pool last week (new house came with pool) and so everything is new. I've not used algeacides yet. I did read about borates in a previous post and asked the lcal shop for them, but they said they didn't cary them and fobbed me off with some excuse.

When I said CA, I meant Cyanuric Acid - guess I don't have the abreviations correct yet. The first month I had the house/pool, it gobbled up chlorine within days and when we turned on the SWG, which was set to 80%, the chlorine has been high (see below) and I've had it set to 50% for 3 or 4 days and it's still high - maybe I can turn it down further. As far as CYA levels, FC levels, etc, I guess i Just have the one control on the SWG which is percentage output, so I'll see how it goes with some more time. Despite my good (?) chlorine levels, I do have some green algae, but its on the rock round the pool, not in the pool itself.

No vinyl pool - its cement based and I'm still trying to work out whether its plaster, gunite or painted cement, not sure how I can tell. Its certainly cement on the outer shell. The inside of the pool is a hard surface with a blue/black hard coating and someone called it plaster. so I don't know.

Anyway, this is turning into a long story, which I was originally trying to avoid. My plan was to ask specific questions. I'll go over your reply a couple of times and try to further my education/experience as time goes on.

Cheers,

Allan.

P.S. its a Goldline Aquat-rite, labelled as a Mineral Springs MS-10, and I managed to download the user manual a few days ago thanks to this forum. I spent several weeks trying to figure out if "minerals" was something other than salt.

P.P.S We just turned the SWG on and the salt level has fallen below 2600 a couple of times, which confused me as I read in this forum that salt doesn't go anywhere. I'm adding 3 more bags of salt right now to try to get it back up to 3200. Texas has had a lot of rain recently, so maybe that's got something to do with it. Only reason I mention this is that despite the salt being low, the chlorine levels are still high, so I'm confident I can turn this baby down lower. I'm also guessing the cell ain't been cleaned in some time so I plan to do that next weekend.

[chem geek]

Allan,

Yes, the salt can go down by dilution -- splash-out or backwash or overflow from rain.

The pool stores do not understand how TA can actually make the pH go up faster. It is counterintuitive and most think that the SWG output itself makes the pH go up, but the usage of the chlorine is acidic (i.e. makes pH go down) and exactly compensates for the rise in pH when the chlorine is generated. Anyway, don't worry about trying to understand it. Just look at it from a practical point of view and if letting the TA level drop has the rise in pH slow down and uses less acid each time, then it just works that way.

Pools and spas are essentially over-carbonated. That's what TA mostly measures -- carbonates (mosly bicarbonate). Just as a carbonated soft drink outgasses carbon dioxide to the air, so does a pool or spa. And just as stirring or shaking a soft drink or blowing bubbles in it through a straw makes it go flat (i.e. lose carbonation) faster, the same thing happens in a pool. The loss of carbonation -- the outgassing of carbon dioxide -- causes the pH to rise.

Don't worry about CA vs. CYA -- at least the number makes more sense now. You didn't have the Calcium Hardness (CH) measured -- that's something you should do since that affects calcium carbonate saturation and with your presumed plaster or plaster-like pool (even if Pebble Tek or other hard surface -- it's certainly not vinyl nor fiberglass).

Algae on rocks that aren't constantly bathed in the pool water is normal and is like algae in the skimmer above the water line. Algae will grow in moist environments and if the water isn't chlorinated, the algae will grow. In my own skimmer, I just wipe it periodically.

Richard

[JerseyJim]

Richard,

I read this response with great interest. I have an indoor pool that at the beginning of summer was both re-plastered and converted to salt. I struggled at the beginning with runaway chlorine levels but finally got that under control by shortening my filtering cycle. I knew that the new plater would require regular addition of Sodium Bisulphate for a while. But my pH is still through the roof.

After reading this response, I now know that hydrogen gas is my issue and you're right... I do see the bubbles. I think my actual problem is the fact that we have an automatic pool cover and it is closed 90 percent or more of the time. We need to keep the pool covered when not in use because of humidity and condensation issues. I'm about to close the pool for the winter. What do I do now to prepare for closing? What do I do when the pool is in operation next season?

I really appreciate finding someone who knows so much about this. My local pool people have no experience with covered pools and the unique problems they have.

JerseyJim

With an SWG, it outputs hydrogen gas bubbles (you can see them readily at night if you run the pump and SWG and turn on an interior pool light) and that aeration causes carbon dioxide to outgas from the pool and that causes the pH to rise. So ironically, a lower TA is better. Mostly, though, you want to figure out a way to lower your chlorine demand so that you can lower your SWG output. Using an algaecide will help and some people use 30-50 ppm Borates in their pool for that reason -- both as an algaecide and as an additional pH buffer that is not carbonate (so won't outgas). So I wouldn't add any Alkalinity Up.

Some SWG manufacturers recommend 60-80 ppm CYA and if your pool gets a lot of sun then that does seem to cut down the breakdown of chlorine from sunlight quite a bit. If you do this, you should set your FC level to around 4.5% of the CYA level (at least). Most SWG pools do seem to operate OK at these lower chlorine levels, but not all do (manually dosed chlorine pools usually need a minimum FC of 7.5% of the CYA level to keep away green algae). Your 4 ppm FC at 40 ppm CYA is more than you need for an SWG pool. So increasing the CYA could help -- or lowering the FC target to 3 ppm can help as well (if it lets you lower your SWG output time).

Using a pool cover to keep the sun's UV rays off the pool will help -- again, if it lets you lower your SWG output.

Finally, if you do keep a lower TA, then a higher pH of around 7.7 compensates to keep calclium carbonate saturation (if you have a plaster pool) and it will also outgas less at the higher pH.

Since you just lowered your SWG output, why not see if things improve just from that -- and let us know. Also, if CA is Calcium Hardness (also abbreviated as CH), then you must have a vinyl pool, is that right? Otherwise, you would need more calcium. With a vinyl pool, you can easily go to a lower TA (even as low as 50), but see how things go with your recent changes of lowering your SWG output and your lower TA.

Richard

[chem geek]

Richard,

I read this response with great interest. I have an indoor pool that at the beginning of summer was both re-plastered and converted to salt. I struggled at the beginning with runaway chlorine levels but finally got that under control by shortening my filtering cycle. I knew that the new plater would require regular addition of Sodium Bisulphate for a while. But my pH is still through the roof.

After reading this response, I now know that hydrogen gas is my issue and you're right... I do see the bubbles. I think my actual problem is the fact that we have an automatic pool cover and it is closed 90 percent or more of the time. We need to keep the pool covered when not in use because of humidity and condensation issues. I'm about to close the pool for the winter. What do I do now to prepare for closing? What do I do when the pool is in operation next season?

I really appreciate finding someone who knows so much about this. My local pool people have no experience with covered pools and the unique problems they have.

JerseyJim

JerseyJim,

The curing of plaster causes the pH to rise as calcium hydroxide is released into the water as part of the curing process. Since your pool is covered, then I would assume that the strong pH rise is mostly due to the curing of plaster and only secondarily due to the SWG hydrogen gas bubbles driving carbon dioxide out of the pool. The greatest rise in pH from curing is during the first month and drops off after 3 months, and should taper off after 6 months though some people report still seeing a rise after a year though that may be from other factors. Also, I would suggest you use Muriatic Acid instead of Sodium bisulfate (dry acid) since you will be adding a lot of acid initially and the dry acid will build up sulfates which might be a problem with the plaster if the levels get too high (I don't know how high precisely when problems occur, unfortunately).

For closing, assuming the pool doesn't freeze over (I doubt it would since it's indoors unless it's in a separate building you don't heat), then you just add a large dose of PolyQuat 60 algaecide (the dose recommended for Initial or fighting algae) IF you are going to be shutting down the SWG due to colder water temps. You can check on the pool periodically and add a little chlorine, possibly once a month. Otherwise, if you keep the SWG running during the winter, you don't need to do anything different than what you did during the summer.

Richard

[coilerman]

Reading this with some interest because I also have a gunite pool with SWG.

Am I reading this correctly - that low TA is normal for a SWG pool? If so, how low? My TA immediately after spring opening is 60ppm. I was going to run out to buy some baking soda to raise that to at least 80ppm but now I'm reading in this post that low TA is normal.

Also, this is the first time I am hearing that sodium bisulfate is bad for plaster/gunite pools. Do you have any details on this?

Thanks.

[chem geek]

You can read about sulfate attack here, but unfortunately I cannot find any source that gives the concentration of sulfate when such problems start to occur.

As for TA, it's not that low TA is normal for an SWG pool but rather that having the TA lower reduces the rate of outgassing of carbon dioxide and that reduces the rate of pH rise. Another option that helps and can be used in conjunction is to add 50 ppm Borates to the pool (if this is added with 20 Mule Team Borax, then Muriatic Acid needs to be added as well; if added with something more pH neutral like Proteam Supreme Plus, then no acid need be added). The Borates are an algaecide and may lower chlorine consumption thereby letting you lower your SWG output. Having the CYA level at 60-80 ppm will also help for the same reason. If you keep a lower TA level (say, 70 or 80 ppm) in an SWG pool, then you'll want to either have a higher CH level or maintain the pH target closer to 7.7.

Richard