New Pool Owner Needs Help

[John450r]

Got my test kit from Leslie's and here's my numbers:

FC: 2.5ppm
TC: Same as FC (2.5ppm), which yields 0 CC. Ideas?
pH: 7.8
TA: 145ppm
CH: 450ppm
CYA: Less than 30ppm

Pool has cartridge filters which I have cleaned, but they do need replacing. Water is crystal clear.

I only have one complaint. The walls of the pool, walls I mean all vertical surfaces, seem to be getting stained a brown-green-grey color. Wire brushing does nothing to the stains and I am at a loss at how to clean it. One thing, the pool has a little bit of dirt at the bottom, I am getting a pool vacuum tomorrow and it will be gone ASAP.

Could my high TA or CH be causing the stains? Or maybe the dirt in the pool?

Thank you got any help.

[chem geek]

You can use The Pool Calculator to calculate the saturation index. With your numbers, it's +0.6 if I use 80F temperature and +0.4 if I use 50F temperature. This is higher than it should be so what you are seeing may be scaling due to the high combination of pH, TA and CH. You can lower the TA by following the procedure described in this post. The CH can be lowered by dilution with water that is lower in CH.

[John450r]

Thank you very much for your quick response. I took your advice and have begun the process described to lower the TA in my pool.

I have a few questions regarding the actual testing I am doing so I want to make sure my measurements are correct.

I'm using the K-2006 test and have questions regarding the TA and CH test.

During the TA test, when I add the titrant, it turns initially red/pink, then fades back to green until I add enough for it to remain green. Is this normal?

During the CH test, the initial color is pink, not red like the instructions state, is this normal? Then, at about 250ppm CH, my sample turns purple. It will then turn blue at 350ppm. The instructions state blue is my endpoint but doesn't mention the purple?

Also, I tested my fill water for CH and got about 200-270ppm CH. (First reading is purple, second is when it turns blue, ref above question).

[chem geek]

The TA test starts out green when you add the indicator dye. When you add titrant, it is red in the vicinity of the drop, but with stirring this disappears. You keep adding titrant until the color holds at red. What you are seeing is normal. You should be swirling a little more to have it mix faster (use a swizzle stick, if you need to).

As for the CH test, you may have a fading endpoint that makes the color harder to distinguish. Try adding some titrant drops to the sample first (say, 2-4 drops) and then follow the procedure adding buffer and indicator and more titrant drops. Add the initial number of titrant drops to your later titrant count. This may help have the endpoint be easier to see.

Your fill water is high in CH so lowering CH by dilution will take a lot of water. That's unfortunate. Also, any evaporation in your pool will simply add to the CH from the fill water. So using a pool cover to prevent evaporation will help you keep the CH lower.

Richard

[Me...]

Sounds like an outdoor Marcite pool? In any event it could be something IN the finish or coming through from behind the finish. Or it could be staining/algae due to improper chemistry at an earlier time.

FC looks good, great to see 0 Combined, TA and CH maybe a tad high but not critical and the CA should be 30-50 but this is only for chlorine longevity not strength. Too much CA will actually weaken it.

That said the pH is high and at 7.8 the chlorine is much weaker than at 7.2.

So maybe the circulation is the culprit? You need to get that 2ppm distributed evenly to allow the chlorine to get to all surfaces. If this was going to be the case, it could be return fitting placement or total filtration flow.

A tip. Test your fill water. This will help to determine the best chemical regime for YOUR pool.

[John450r]

Thank you both for your help. Here are some numbers from today. This is after following the method described to lower my TA by lowering pH, aerating, lowering, and so on.

FC: 2.5ppm
TC: 2.5ppm (Still 0 CC)
pH: 7.5 (been moving it from 7.0 to 7.5 for a week or so)
TA: 115ppm
CH: 300ppm
CYA: Less than 30ppm

I am 100% confident in my FC, pH, and TA readings. I am becoming more confident in my CH readings as I have begun adding 5 drops of titrant to the test before the buffer/indicator. It is allowing me to get a blue end point earlier. But.... I am still getting a purple solution before it turns blue. Purple at 10 drops (250ppm) and blue at 12 (300ppm).

Okay, other than what I asked above. I have one more question...

During the CYA test. I am filling the little bottle to 7ml, filling the rest with the solution to 14 mil, and shaking it for 30 seconds. The water does not get cloudy enough to make the black dot disappear at the bottom of the comparator tube. It probably makes it halfway disappear, but should it be completely invisible due to the cloudiness of the solution?

Does this just mean I have very low levels of CYA or am I doing the test wrong?


Thank you very much for your help.

[chem geek]

Your CYA is below 30 ppm. See this link for some photos of how the black dot should disappear when you've added enough solution to the tube. There are some CYA tests that have longer tubes that can measure to 20 ppm, but at any rate, your CYA is low.

It's good that you got your TA lowered. I'm not sure why your CH dropped unless it's just due to your getting a sharper endpoint. Be sure and let each drop in the test thoroughly mix by swirling. It's a slow test when done properly.

Your saturation index is much better now. Perhaps Me... has some suggestions for getting rid of your stains. At least you shouldn't be getting any scaling with your new numbers.

What are you using as your source of chlorine?

[Me...]

For now all I could think off would be to get your tap/fill water tested for metals/minerals. Every pool store would carry products to both remove them from the water and from the surfaces. It doesn't always work but there are many success stories.

So if you find you have metals/minerals in your fill water you would want to be adding a maintainence dose of something. If the stains turn out to be from that source, use a different product to try and "sponge" the stains back off the wall. Also possible the product applied to the walls, marcite, colorquatz etc might have had impurites that were oxidized initially. There has been success with those types of staining also also.

[John450r]

I believe the reason my CH is lower is only because of the difference in testing as you mentioned.

Thank you very much for the link reference the CYA test. Should I do anything to raise my CYA?

I am chlorinating with liquid chlorine.

Reference the minerals/metal in my fill water, will a pool supply store be able to test this for me?

I also am not if my pool is marcite or not. Is their anyway to find out? The finish is smooth to the touch, blue/white in color. I don't know if a picture would help at all.

[chem geek]

If your pool is exposed to direct sunlight, then you should have more CYA. 30-50 ppm is good unless you have a lot of sun as in a desert area in which case you can go higher, but not more than 80 ppm. In any event, you should not let the FC go below 7.5% of the CYA level if you want to prevent algae growth.

You can either buy some pure Cyanuric Acid (CYA) which dissolves very slowly -- some people add it slowly to the skimmer and let it dissolve in the filter with the pump continuously running, but you need to not backwash for a week to ensure it all dissolves. Alternatively, you can put the pure CYA in a sock and hang it over a return flow in the pool.

A faster way to add CYA is to get some Dichlor chlorine and use it for a while. For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm. It dissolves relatively quickly.

Another approach is to use Trichlor pucks/tabs for a short time. For every 10 ppm FC added by Trichlor, it also increases CYA by 6 ppm. It dissolves slowly and is used in a floating feeder. It is highly acidic. Probably not the best choice for you unless you are willing to add Borax to compensate for pH.

As for minerals, specifically metals such as iron and copper, yes your pool store should be able to measure that.

Richard