chem geek said:
I have Metal Magic and will try this test overnight. I will go to the local pool store and see if I can get some phosphate remover and try that test tomorrow.
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- Thread starter andy
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I have Metal Magic and will try this test overnight. I will go to the local pool store and see if I can get some phosphate remover and try that test tomorrow.
Andy,
Sorry I confused you with the 1/10th per gallon vs. 1/4 teaspoon per 4 gallons. Anyway, your use of 0.4 and the result are fairly consistent so that's good.
It's interesting that the thiosulfate wipes out both the chlorine and the combined chlorine in terms of measurement. This may just mean that when you add the third reagent to test the CC that the thiosulfate gets to the freed up chlorine before the reagent (iodide) does so it prevents it getting measured. Oh well, it was worth a shot, but now that I think about it, it was a hair-brained idea. Basically, it means that without the Taylor K-2041 MPS interference remover, we can't really see the results of the MPS test but I would bet the MPS isn't really getting rid of existing CC -- it's designed to prevent CC formation in the first place, not to get rid of existing CC. It was certainly interesting to see that high MPS levels registered as FC and not as CC...that's not something commonly known in the industry that thinks instead that MPS shows up primarily as CC in the tests.
So yes, try the metal magic next and then in a separate test the phosphate remover, just in case either the metals or the phosphates are causing some sort of test interference.
waterbear knows testing better than anyone on this forum -- he's also seen tests been done wrong so has an eye out for that sort of thing and I'm sure was only trying to help (his bio is here). I'm still leaning towards this CC either being pretty stuck and hopefully not an issue or being a false reading from interference -- the two next tests will help eliminate some of the interference possibilities.
Richard
Sorry I confused you with the 1/10th per gallon vs. 1/4 teaspoon per 4 gallons. Anyway, your use of 0.4 and the result are fairly consistent so that's good.
It's interesting that the thiosulfate wipes out both the chlorine and the combined chlorine in terms of measurement. This may just mean that when you add the third reagent to test the CC that the thiosulfate gets to the freed up chlorine before the reagent (iodide) does so it prevents it getting measured. Oh well, it was worth a shot, but now that I think about it, it was a hair-brained idea. Basically, it means that without the Taylor K-2041 MPS interference remover, we can't really see the results of the MPS test but I would bet the MPS isn't really getting rid of existing CC -- it's designed to prevent CC formation in the first place, not to get rid of existing CC. It was certainly interesting to see that high MPS levels registered as FC and not as CC...that's not something commonly known in the industry that thinks instead that MPS shows up primarily as CC in the tests.
So yes, try the metal magic next and then in a separate test the phosphate remover, just in case either the metals or the phosphates are causing some sort of test interference.
waterbear knows testing better than anyone on this forum -- he's also seen tests been done wrong so has an eye out for that sort of thing and I'm sure was only trying to help (his bio is here). I'm still leaning towards this CC either being pretty stuck and hopefully not an issue or being a false reading from interference -- the two next tests will help eliminate some of the interference possibilities.
Richard
andy said:
OK here are a few of my thoughts. First of all this is a swimming pool and not a science experiment so get a grip! (Sorry if that sounds rough but too many people get hung up on the small stuff and forget to see the big picture! It's a pool, not the space shuttle!)
Now for a few constructive (hopefully) observations.
CYA messes up ORP readings. Very low levels of CYA are probably not going to make much difference but be aware that this is one of the biggest drawbacks to ORP controllers in swimming pools. Also, both the ORP electrode and the pH electrode need to be properly calibrated (and this can actually take some time to do properly, which is why I don't think they are the best thing for residential pools unless you really understand the science behind them.) I suspect that yours might be out of calibration given the pH discrepancies you keep reporting between the pH readings and the phenol red pH test.
If there are no phosphates in your fill water then the phosphates most likely came from the phosphonic acid based Metal Magic, which can convert to orthophosphates in the water. You said you had brown stains. These are usually indicitive of iron but you also said that you have a fiberglass pool and copper can cause brown staining on fiberglass. If you have a heater that has a copper heat exchanger it could be a source of the copper. Might be worth while to have your water tested for metals but be aware that the sequesterant will mask the test results if you are still using it. Also, you said that after shocking you had a sand like grit in the pool. You did not say what you used for shock (cal hypo, sodium hypochlorite, etc. but be aware that high chlorine levels can cause metals to precitpitate out of solution and that cal hypo can cause calcium carbonate to precipitate out also. Either one could look like a grit on the bottom of the pool but the metals would most likely have a color and the calcium would be white. I would not worry about using a lanthanum based phosphate remover since you do not have a problem with algae or not being able to maintain a proper FC or ORP reading. The only way that I know of that phosphates can contribute to CC is by allowing algae to bloom and the residual chlorine cannot take care of it. Since this is an indoor pool I assume it's exposure to sunlight is minimal so I would not expect algae blooms to be a major problem. However, a pool with high phosphates might also have high nitrates/nitrites and these can cause persistent CCs.
Keeping a pool covered all the time will lead to persistent CC formation in the water. Uncovering the pool and keeping it uncovered for a period of time can help by allowing the volatile CCs to gas off but an indoor pool often has a problem with persistent CC since the atmosphere above them is a closed system unless the ventilation system is really excellent. Since you are using ORP controllers I would not recommend using MPS. This will mess up your ORP readings and cause too low a chlorine level for properly sanitized water! ORP measures the oxidation potential of the water and MPS is an oxidizer but NOT a sanitizer.
Now as far as your testing methods....I can help you with the CH test, which most people do wrong. If you are getting a purple color that is known as a 'floating endpoint'. It is often caused by metals in the water. Since you have been using Metal Magic I assume you have a metal problem (otherwise there is no reason to be using a sequesterant). You mentioned brown staining, which is often from iron.
To test the CH first add 6 drops of the calcium titrant (3rd reagent) to your 25 ml sample and swirl well (about 20 seconds).Be sure to include these 6 drops in your drop count for the titration. Next add the 20 drops of calcium buffer (1st reagent) and swirl well. It is important to mix these well and give them time to react. Now add 5 drops of the indicator and swirl to mix. Now the important part of how to do this test. Add a drop of titrant and swirl for 20-30 seconds before adding the next drop. You need to swirl the vial between each drop for 20-30 seconds. If you do this you will not get an indistinct purple color which, if you look close is actally purple 'floaties' in a blue liquid. It takes a while to do this test properly, especially if your calcium levels are high. The only way to speed up this test is by using a magnetic stirrer to insure complete mixing of the titirant.
A few other observations. I would lower the TA a bit, expecially since your calcium is at 400 (and might possibly be much higher since you have never reached a true endpoint. )
To know when a titration test is done you keep adding titrant until adding one more drop does not produce any additional color change and then you don't count that last drop.
Finally, I find the fact that your CC seems to stay constant at .8 ppm no matter what you do indicates one of a few possible things. The first is testing error. I would have someone else do the test with your kit and see what they get. The second is that there are some non volitle CCs in the water that are only going to be removed by 'nuking' the pool with extremely high chlorine levels or by draining and refilling. I would recommend testing the water for nitrates and nitrites (Not normally done with pools but can cause either a large chlorine demand or persistant CCs.) You can use an aquarium test kit to test for the nitrates and nitrites. Ideally they should be both be at 0 ppm. Unfortunately, the only way to lower nitrates and nitrites is by draining and refilling.
If it were my pool the first thing I would do is make sure my electrodes are properly calibrated. The second thing I would do is keep the pool uncovered for at least a few weeks to see if the CC readings change. I would stop using a sequesterant if I did not have metals in the water but I would not worry about using a phosphate remover at this time. I would test the water for nitrates and nitrites and if present would drain and refill to get rid of them.
Finally, if all else fails I would accept the fact that many indoor pools have a high level of CCs that are persistent and that mine might just be one of them.
Your situation is complicated by the fact that you are using ORP controllers so that really removes a few of the options at your disposal. Keeping your pool uncovered is probably your best course of action, combined with regular shocking with liquid chlorine. You might need to go higher than the 10 ppm that would be customary in an unstabilized indoor pool,however.
andy said:
IF you cannot leave the pool uncovered you are basically SOL so to speak because you will find it difficult to impossible to lower your TA and you will probably never get rid of the persistant CC problem.
Sorry!
Another possibility is that your test kit is bad. You might try an experiment. Get a gallon jug of distilled or deionized water. Add a drop of bleach to it, and then check for free and total chlorine. They should be equal. If not then the problem lies with your test kit.
Now that the holiday is over I'll try and catch up on some of the tests I need to get done. I was able to find the nitrate and nitrite test kits at the pet store today and also was able to get an accurate CH test done. I am trying a new chart that should make viewing my recent test results easier. I'll try to get some of the other tests we talked about done also.
Recent tests done:
Bucket test with pool water and metal magic. No change in CC
Nitrate test = 0
Nitrite test = 0
Recent tests done:
Bucket test with pool water and metal magic. No change in CC
Nitrate test = 0
Nitrite test = 0
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So that is 30 amp/hours over five days or 6 amp/hours per day, which means the cell is active for just under one hour each day (average). That should be on the order of one oz of chlorine per day. Even if my math is a little off that sounds like a reasonable amount of chlorine usage for an indoor pool.
I have decided to remove the SWG and go to regular water. The corrosion the salt is causing will only get worse and eventually destroy my automatic cover componants along with the damage it is doing to my coping stones. I hate to do this but I feel it is the correct decision in my case.
Can I remove the SWG cell and keep the PH sensor and acid pump to maintain my PH level?
Can I remove the SWG cell and keep the PH sensor and acid pump to maintain my PH level?
The PH sensor and acid tank/pump will work without the SWG, but that might not turn out to be useful. The PH regulation depends on the SWG cell to raise the PH through aeration and it then lowers the PH with the acid pump. Without the aeration from the SWG cell you won't have anything keeping your PH from getting too low. The PH sensor and acid pump/tank will keep the PH from going too high, but that won't fully regulate your PH without the SWG cell running.
By the way, you don't actually have to remove the cell, just disable ORP and set the percentage to zero. There will be constant add salt messages on the display once you remove the salt but the PH system should still work. (I have never actually tried this however.)
Another thing to keep in mind, replacing the water and switching to a different chlorine source will lower the salt level dramatically but it will still climb slowly. Chlorine turns into salt after it reacts with contaminates in the pool and salt is shed from the skin of people swimming in the pool. It is not uncommon for pools without any manual addition of salt to have salt levels between 500 and 1000. So, there should be some improvement in the salt problems, particularly at first, but they won't necessarily go away completely.
By the way, you don't actually have to remove the cell, just disable ORP and set the percentage to zero. There will be constant add salt messages on the display once you remove the salt but the PH system should still work. (I have never actually tried this however.)
Another thing to keep in mind, replacing the water and switching to a different chlorine source will lower the salt level dramatically but it will still climb slowly. Chlorine turns into salt after it reacts with contaminates in the pool and salt is shed from the skin of people swimming in the pool. It is not uncommon for pools without any manual addition of salt to have salt levels between 500 and 1000. So, there should be some improvement in the salt problems, particularly at first, but they won't necessarily go away completely.
To completely control PH you need a way to raise the PH when it is too low and to lower the PH when it is too high. The Total Control system uses the SWG cell to raise the PH and uses an acid tank/pump to inject acid to lower the PH. The cell is constantly raising the PH and the acid additions are regulated to bring the PH back down to the desired level. Without the SWG cell there is no process that will raise the PH, so it becomes possible for the PH to fall lower than desired.
When a SWG cell is operating it will inject hydrogen bubbles into the water as a side effect of the chemistry happening inside the cell. These bubbles cause aeration of the water which allows some CO2 to come out of solution which raises the PH. This happens because swimming pools are normally operated well out of equilibrium. The TA level combined with lower than equilibrium PH level causes CO2 to be dissolved in the water at higher than equilibrium levels. CO2 out gassing from the surface of the water is very slow, so the water can normally be held out of balance like this for months at a time. The hydrogen bubbles increase the rate of CO2 out gassing, raising the PH closer to equilibrium levels. Between the CO2 out gassing and the acid additions required to maintain the PH the TA level will slowly fall over time.
When a SWG cell is operating it will inject hydrogen bubbles into the water as a side effect of the chemistry happening inside the cell. These bubbles cause aeration of the water which allows some CO2 to come out of solution which raises the PH. This happens because swimming pools are normally operated well out of equilibrium. The TA level combined with lower than equilibrium PH level causes CO2 to be dissolved in the water at higher than equilibrium levels. CO2 out gassing from the surface of the water is very slow, so the water can normally be held out of balance like this for months at a time. The hydrogen bubbles increase the rate of CO2 out gassing, raising the PH closer to equilibrium levels. Between the CO2 out gassing and the acid additions required to maintain the PH the TA level will slowly fall over time.