Pool Calcium levels

Several months ago we moved into a beachfront house with a VERY large pool--about 33,000 gallons. I have been maintaining it. It tends to prefer a 7.8 pH, which may be the local water. I balance with occasional muriatic acid, and I use a liquid sodium hypochlorite chlorine solution. The pool maintains chlorine level pretty easily, even though it is an outdoor pool. The stabilizer level is a quite steady 100. I have been advised by the pool company where I test my pool water to add sodium bicarbonate from time to time to balance overall alkalinity. The pool is clear, balanced, and wonderful to swim in.

However, the calcium levels seem to be creeping up: it has maintained between 340 and 480, and recently jumped up to 680. The pool company is recommending Cal-Treat, but I am reluctant as the pool is very clear. There is a darkening of some of the tile around the waterline, which can't be brushed off (I brush the waterline weekly).

Advice, please?

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Originally Posted by beachfrontpool

Advice, please?

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Yes.

1. With a pH of 7.8 and CH of 680 ppm, do NOT add any bicarb! And, put whoever told you to do that into the "cannot be trusted to give pool chemistry advice" category!

2. Get a testkit, a K2006, and test BOTH your pool water AND your fill water. Links below. You're getting some pretty dodgy advice, and the chances are good you're also getting some dodgy water testing. It's unlikely your CYA is a "steady" 100; it's more likely, it's a steady greater-than-100 . . . and the difference matters.

3. Complete the Pool Chart.

4. You DO need to lower your CH level, IF it really is 680, and you do NEED to stop the scaling. But FIRST, you need to figure out where the calcium is coming from. Nothing you've described putting in your pool adds calcium, so some critical information is missing here.

5. Lower your pH; keep it nearer 7.2 till you know what's going on with your pool. . . . and do NOT add bicarb or soda ash (pH Up). If you accidentally OD with acid, add borax to raise the pH back above 7.0.

Ben

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+ Get a cheap OTO (yellow drops) / phenol test kit, or if available at YOUR Walmart (check availability), get the HTH 6-way DROPS test kit, which is compatible with the Taylor K2006. Test the pool as soon and you can, and post the results. If you get the 6-way kit, ALSO test the water you FILL the pool with, especially if it's a well, and post THOSE results as well. (The HTH is the best available kit you're likely to find locally, but it's not the K-2006. It can only provide rough measurements chlorine levels above 5 ppm, and it measures "TOTAL" hardness, rather than "CALCIUM" hardness, which is not ideal.)

+ Having a good test kit makes pool care easier for EVERYONE, but is an ESSENTIAL tool for pools with problems. A good test kit means a kit that can test chlorine from 0 - 25 ppm, pH, alkalinity, calcium hardness, and stabilizer with reasonable accuracy. Test strips (AKA 'guess-strips' ) do NOT meet this standard. Some pool store testing is accurate; most is not. The ONLY way you'll know whether your pool store is accurate or bogus, is by testing accurately your own self. On the other hand, pool store 'computer' dosing recommendations are NEVER trustworthy -- ignore them. They are designed to sell more chemicals than you need, and WILL cause many pool problems.

+ We recommend the Taylor K-2006 test kit, which meets the requirements above, for many reasons. The HTH 6-way drops kit is a great starter kit, and is compatible with the K2006 (it's made by Taylor). There are a few alternatives; for example Lamotte makes an FAS-DPD kit that's OK -- but it costs 3x as much. But, we're not aware of any test that is better, and since we are all familiar with the K-2006 (and can help you with it) we recommend it exclusively ( Test kit info page )

One caution for the 2012 season: Amazon does not stock the kits directly. So when buying at Amazon, Amato is our current preferred seller. However, they often don't list enough stock to last the whole day, so try order mid-morning. You should expect a delivered cost under $60 for the K2006A and under $95 for the K2006C. If you can't find that, wait a day.

+ Here are links to the kits we recommend (you can check local availability on the HTH kit, using the Walmart link):

HTH 6-Way Test Kit @ Walmart
Taylor K2006A (3/4 oz bottles) @ Amazon
Taylor K2006C (2 oz bottles) @ Amazon

Thanks, Ben. To date I've been using All Clear 2 step OTO and phenol red for home chlorine and pH testing only, and the rest is tested at the pool shop. I just ordered the Taylor 2006C kit from Amato, and will learn to do it myself. Will report results when new kit arrives.

good deal!

If you have been relying on pool store testing there is a very good chance that the CH is not that high and it is testing error. Not uncommon at all. Once you do get your kit do the calcium hardness test with a 10 ml water sample, 10 drops of calcium buffer and three drops of indicator (instructions in small print in the lid of the test kt at the bottom of the calcium hardness test section). This way every drop of titrant will equal 25 ppm CH instead of 10 ppm so the test will go much faster for your suspected high calcium levels and you will see the color changes more readily.

Just got the Taylor kit, and tested all: CH = 800 ppm(!), and the city water input tested at 110 ppm; CYA = 62; Alkalinity = 60. Chlorine and pH were both good, 4.0 and 7.3, I just added sodium hypoclorite and muriatic acid yesterday--it's been quite rainy the last couple days. I can't understand why the calcium is creeping up.

I haven't shocked the pool since we bought the place in May--is this necessary? What does it actually do? The pool doesn't get heavy use--we are only two using this big pool. We just bought new filters--they system takes 2 of the Hayward Star 1200 series. Does filtration affect calcium in concrete pools in any way?

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Originally Posted by beachfrontpool

ust got the Taylor kit, and tested all: CYA = 62

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How did you get this reading with the Taylor kit? It is only able to give a CYA reading to 10 ppm and since the measurement scale is not linear, interpolation between the markings is not goin to be any more precison than 5 ppm (and even that is a guess.)

Yes, the kit is a bit complicated, and I am certainly no chemist. However, the reading levels they advise you to refer to at the back of the comparator tube for the CYA readings range from 30 to 100, where cloudiness obscures the black dot, and 60 was about where it disappeared.

There are two ways you can remove calcium from your pool:

1. Drain 2/3 of the pool, and refill. With pool water CH=800 and fill water CH=110, you should end up with new pool water CH=340, which is acceptable. BUT, be careful to make sure your pool won't float! Dig a 3' deep hole next to the pool, and make SURE it does not fill with water. If it does, don't drain! Empty concrete pool WILL float on a lake OR in ground water!

2. Do lime softening, which involves raising the pH above 10.5 with soda ash, and precipitating the calcium as calcium carbonate, and then vacuuming it out. You'll need to be comfortable using the K2006, and be able to vacuum to waste, before you're ready to tackle this. This will remove more of your calcium, but will be more work. There's a bucket test you MUST do first, to make sure it will work, and that you have the right doses.

Meanwhile, keep your pH between 7.0 and 7.4.