Can my chlorine be high while SWCG output is low??

[Jodester]

Hi, all --

Just converted to a SWCG pool this summer when we replaced our vinyl liner. I've been working on the water balance to try to allow the generator to cycle on as little as possible and still maintain healthy sanitizer levels, to prevent ph rise. I've been trying to follow Waterbear's "Fine Tuning a Salt Water Pool" suggestions and have been getting some success (TA down to 120 from 150). Before I go any further, here were my levels yesterday, as tested with my brand spanking new Taylor K2006 test kit:

FC: around 11 ppm
CYA: around 75 ppm
PH: around 7.7
Hardness: around 300
TA: 120
Salt according to CompuPool CPSC36: 3200 (tends to fluctuate, though, between 3100 and 3900 -- Aquachek strips more consistently show around 3700)
25,000 gallon inground pool with attached "waterfall" spa

I thought that 11 ppm for FC seemed a little high, even with my CYA levels at 75, and that was with the generator running at 30%. So I lowered it to 20%, and will test FC today to see what happens. Is this okay -- to be running the output so low, even 30%, and having FC so high?

It should also be noted that before I got my K2006 kit, I was using Leslie's (made by Taylor) DPD reagent kit, and would get a high FC color match (over the max), but within about 30 seconds the pink color would fade to more like 2-3 ppm. Does this mean anything?

As a side note which may offer useful info to you experts in getting a total picture of my pool, I had been working on lowering the TA to closer to 80 using Waterbear's suggestions, adding dry acid a little at a time and running the spa jets once I brought the PH down to the 7.2 range. However, I have not been able to do this constantly since we can only run the spa jets when the whole pool is on (otherwise the water level in the spa drops to below the jets), and since I leave for work in the morning before the timer turns on the filter pump, I have not aerated the pool nor added any dry acid for about a week. Would running the filter and spa jets 24/7 (and thus the SWCG) be okay when trying to lower TA, and if so, how many days do you think it would take? I'd hate to inflate my electric bill too much.

Thanks --
Jody

[waterbear]

Hi, all --

Just converted to a SWCG pool this summer when we replaced our vinyl liner. I've been working on the water balance to try to allow the generator to cycle on as little as possible and still maintain healthy sanitizer levels, to prevent ph rise. I've been trying to follow Waterbear's "Fine Tuning a Salt Water Pool" suggestions and have been getting some success (TA down to 120 from 150). Before I go any further, here were my levels yesterday, as tested with my brand spanking new Taylor K2006 test kit:

FC: around 11 ppm
CYA: around 75 ppm
PH: around 7.7
Hardness: around 300
TA: 120
Salt according to CompuPool CPSC36: 3200 (tends to fluctuate, though, between 3100 and 3900 -- Aquachek strips more consistently show around 3700)
25,000 gallon inground pool with attached "waterfall" spa

I thought that 11 ppm for FC seemed a little high, even with my CYA levels at 75, and that was with the generator running at 30%. So I lowered it to 20%, and will test FC today to see what happens. Is this okay -- to be running the output so low, even 30%, and having FC so high?
IF the FC is high you lower the output and/or the pump run time. You are on the right track! It will take a bit of time for the pool to stabilize so don't rush this process. I run my Aqualogic at about 8% to 15%, depending on the ambient temperature, with an 8 hour pump run time to maintain my FC at 5 ppm. My pool is open "year round".

It should also be noted that before I got my K2006 kit, I was using Leslie's (made by Taylor) DPD reagent kit, and would get a high FC color match (over the max), but within about 30 seconds the pink color would fade to more like 2-3 ppm. Does this mean anything?
YES! It means your FC is above 10 ppm! DPD will bleach out at high FC levels and when you see a "flash" of pink that fades or disappears you are seeing this bleachout effect and it means your FC is hgh. When using a DPD test you would now need to start diluting your sample with distilled water and then multiplying your test results by the dilution factor to get anything meaningful. Sounds like you have been runnning a high FC for a while and did not realize it. You can turn off the SWCG until the FC drops to the proper level and then turn it on and fine tune it. Don't be surprised if the FC does not drop for several days. You might not have a big chlorine demand at the moment.

As a side note which may offer useful info to you experts in getting a total picture of my pool, I had been working on lowering the TA to closer to 80 using Waterbear's suggestions, adding dry acid a little at a time and running the spa jets once I brought the PH down to the 7.2 range. However, I have not been able to do this constantly since we can only run the spa jets when the whole pool is on (otherwise the water level in the spa drops to below the jets), and since I leave for work in the morning before the timer turns on the filter pump, I have not aerated the pool nor added any dry acid for about a week. Would running the filter and spa jets 24/7 (and thus the SWCG) be okay when trying to lower TA, and if so, how many days do you think it would take? I'd hate to inflate my electric bill too much.

Thanks --
Jody

If your water level drops when running the spa jets then start looking for a leak or possibly a back check valve in the spa return line.
Adding dry acid "a little at a time" is not going to do the job. You need to drop the pH to 7.0, test TA, then aerate to bring it above 7.4 and repeat this until the TA is on target. You do not need to aerate but it will take longer for the carbon dioxide to gas off. There are other ways to aerate besides using your spa jets BUT if your water level drops when running the spa jets then start looking for a leak or possibly a back check valve in the spa return line.

[Jodester]

If your water level drops when running the spa jets then start looking for a leak or possibly a back check valve in the spa return line.
Adding dry acid "a little at a time" is not going to do the job. You need to drop the pH to 7.0, test TA, then aerate to bring it above 7.4 and repeat this until the TA is on target. You do not need to aerate but it will take longer for the carbon dioxide to gas off. There are other ways to aerate besides using your spa jets BUT if your water level drops when running the spa jets then start looking for a leak or possibly a back check valve in the spa return line.

Oh, no, my water level isn't dropping while the system is on. It's just that once the filter pump shuts off, water stops pumping into the spa (which is what creates the waterfall), and then the water in the spa "seeks its own level" with the pool. I was told by the pool company that this is normal. Is that wrong?

BTW, you're probably right about not having a big chlorine demand right now. I'm on Long Island, NY, and the weather is turning cool as well as having some cloudy, rainy days. We keep our pool open into October because we use the spa at night in cool weather, but we'll be closing it fairly soon. We did have warm weather the past two weekends, heated the pool, and did swim all day, though. Our pool temp had been up to about 90 last weekend; now it's down to about 65. Cooler water and less sun means less chlorine demand, right?

[waterbear]

Oh, no, my water level isn't dropping while the system is on. It's just that once the filter pump shuts off, water stops pumping into the spa (which is what creates the waterfall), and then the water in the spa "seeks its own level" with the pool. I was told by the pool company that this is normal. Is that wrong?
You should have a check valve plumbed into the spa return so the water in the spa does not drop when the spa is off. They might have left it out but it's pretty standard in spillover spa setups. It's not an expensive item so it's normally included. See if you have one and if you do see if it's operating properly. The Jandy and Pentair ones are pretty easy to repair. Just unscrew the screws and take the broken guts out and replace it with the working guts from a new valve of the same kind. It's actually usually cheaper than getting the rebuild parts! IF you don't have a check valve I would consider adding one.

BTW, you're probably right about not having a big chlorine demand right now. I'm on Long Island, NY, and the weather is turning cool as well as having some cloudy, rainy days. We keep our pool open into October because we use the spa at night in cool weather, but we'll be closing it fairly soon. We did have warm weather the past two weekends, heated the pool, and did swim all day, though. Our pool temp had been up to about 90 last weekend; now it's down to about 65. Cooler water and less sun means less chlorine demand, right?

That is correct!

[CarlD]

Yes, unless you plan on heating your pool all winter it's a good time to close the pool...I'm over in NJ, due west of the Lincoln Tunnel so I've got the same weather as you. I JUST closed yesterday as the water kept going into the 70's.

[Jodester]

Time for an update:

So, I turned off my cell on Sunday afternoon, and I just tested my water this evening (Wednesday). The chlorine is down a little, but only a little -- to 8.5 from 11. My ph is holding steady at about 7.6, and the alkalinity is also holding steady at about 120.

Just want to double check about putting in dry acid -- I thought there could be lots of problems if I put in more than a certain amount at a time. According to the chart on the dry acid, in order to lower my ph to 7.0, I'd have to add way more than the recommended amount at once to do it in one shot. Any advice? (Again, I have a 25,000 gallon pool).

-- Jody

[CarlD]

If you are closing, I would NOT lower pH. In our area, over the winter, your pH will go down as the rain and snow melt are slightly acidic. Besides, the only reason to lower a pH of 7.56 is if you are lowering Total Alkalinity.

[waterbear]

Just want to double check about putting in dry acid -- I thought there could be lots of problems if I put in more than a certain amount at a time. According to the chart on the dry acid, in order to lower my ph to 7.0, I'd have to add way more than the recommended amount at once to do it in one shot. Any advice? (Again, I have a 25,000 gallon pool).

-- Jody

If you need to lower your pH by a certain amount you need to add enough acid to lower the pH. Period. How much you need will depend in part on the current total alkalinity. If it is high you will need more acid. if it is low you will need less,. The only way to know how much you REALLY need is to use an acid demand test such as found in the Taylor k-2106 test kit. A rule of thumb is that 1 pt per 10k gal will lower the pH by .2 to .6, depending on the TA and whether borates are present. Like i said the only way to REALLY know is with an acid demand test. An alternative is to add a fixed amount WITH PUMP RUNNING, wait an hour, retest pH, and repeat until pH reaches desired goal. Not as exact or as quick but workable.

Dry acid should always be predissolved in a bucket of water (where it forms sulfuric acid, btw).

Also, with a SWCG it is better to use muriatic acid instead of dry acid. Dry acid will add sulphates to your water and these can be damamaging to some salt water cells. Muriatic acid is also less expensive and more effective (less is needed for the same pH drop.)

[Jodester]

Dry acid should always be predissolved in a bucket of water (where it forms sulfuric acid, btw).

Also, with a SWCG it is better to use muriatic acid instead of dry acid. Dry acid will add sulphates to your water and these can be damamaging to some salt water cells. Muriatic acid is also less expensive and more effective (less is needed for the same pH drop.)

I do pre-dissolve the dry acid in water.

I got kind of scared away from muriatic acid after hearing about all the safety precautions in handling and storing it -- not keeping it indoors, even in a shed; keeping the container wrapped in plastic and then also stored in a covered garbage can; the fact that the pool store itself says they don't sell it as indicated by law; wearing a mask when handling. Are my fears founded?

[aylad]

Muriatic acid is something to be respected, but if you are careful with it, as with any other chemical, it's okay. I don't know why the storage in a covered garbage can precaution--as long as you can contain any spills as well as the fumes, then the garbage can is not necessary. I keep mine in the jug it is sold in, with the cap on tightly, inside a WalMart bag, and I keep it in my garage. I have had no problems with storing it that way, whatsoever.

You do need to be careful when you use it--if you spill it on a concrete deck and don't wash it off, you'll find pits in your concrete. However, if it splashes on your hand, it doesn't start to instantly disintegrate, like some would have you believe--all you have to do is stick your hand in the pool and wash it off, and all is well. The real danger when dealing with this stuff, other than getting it in your eyes, is breathing the fumes. They ARE dangerous, and I can tell you from experience that if you get a good whiff of them, it is a very painful experience. When you open the container, the fumes are usually visible--look like smoke-- so as long as you stay upwind of them, then there is no problem. I usually hold my breath while pouring, though, just to be on the safe side. Only takes once.....

Long story short, if you store it with the cap on where it can't spill, and wear gloves and eye protection and stay upwind of the fumes, then it's a perfectly good, efficient chem to use to lower pH (and more cost effective than trying to use dry acid). I just pour it slowly into the return stream from a plastic measuring cup that I have dedicated to pool use, and it works quite well. Thoroughly wash off any spills/splashes, and you'll be fine.

By the way, if you have a Tractor Supply Co store near you, they are the cheapest source for muriatic that we have in this area--a good bit cheaper than Lowe's and Home Depot.

Janet