CH rising?

[CarlD]

I, on the other hand, am baffled by the rising calcium hardness. Nothing you are doing should cause that.

So...Next question: Is your waterfall fiberglass, too, or is it stone and even mortered?

[chem geek]

Carl,

That's an excellent question (and I, too, look forward to hearing the answer) because normally the slightly corrosive water wouldn't be expected to dissolve calcium carbonate, but perhaps the extra physical erosion of a waterfall might accelerate that process. The problem is that the amount of calcium rise he is seeing is inconsistent with the amount of carbonate that must also be introduced and this should increase the TA and pH and require a lot more acid than is being added to have his TA actually drop from 80 to 70.

If I use the pool numbers given, then adding 7 ounces every other day for for 19 days is 8.3125 cups of 31.45% Muriatic Acid. I can then reproduce maintaining a pH of 7.6 and having the TA drop from 80 to 70 if I assume corrosion of calcium carbonate of 18.9 ppm and a large outgassing of carbon dioxide.

So SOME increase in calcium of around 20 ppm can be explained through corrosion, but not an increase of 70 ppm unless there is some strong acid somehow getting added to the pool (which I doubt -- beyond the Muriatic Acid, of course). I'm betting that the calcium test is off a bit, possibly due to temperature dependence and I'll be eager to see his new measurements.

Richard

[CarlD]

But if it's ALL fiberglass, where the HECK is the Calcium coming from??????

[DONNIE]

My fountain is called a Wok Waterfall. It's basically a 36" wok shapped dish that cascades into the pool with a fall of about 10". It is made entirely of fiberglass BUT...I have put 24 pounds of smooth, flat river rock in it mainly just for weight. Probably 24" diameter and 3" deep. I will retest tonight and post the results. Could the rocks be a source of calcium? I don't believe they are very porus. Each is about 2 to 3" round and 1/2" thick.

Donnie

[chem geek]

If the rocks are like those found in river beds, then they don't dissolve much and are composed of many different minerals, not just calcium carbonate. If they are more like limestone, then certainly soft limestone can wear quickly and is composed mostly of calcium carbonate. Personally, I doubt that the rocks are contributing much to the calcium so my take is that the test is wrong for whatever reason and that the calcium did not in fact increase over that short period of time.

Richard

[DONNIE]

I'm hoping your right. We'll see tonight.

[DONNIE]

Ok. Ok. Took extra care to fill my test bottle to exactly 25ml. Let stand (capped) for 1 hour to get to room temp. Added 2 drops of titrant before test. Added the 5 drops of blue which took about 30 seconds to totally mix. Started adding my drops very carefully to be exact. At drop 41 (counting the first 2) it turned slightly purple. drop 42 turned a distinctive blue. Drop 43 & 44 produced no change. So voila...CH=420ish. I guess the 41 degree water made the difference. Or maybe it was the wine! Lesson learned. DONT TEST 41 DEGREE WATER! Thanks Richard. Thanks Carl. I appreciate the concern and especially the guidance.

Donnie

[waterbear]

I've said it before and I will say it again, water temp makes a difference. If you compare test results done of 75 deg water and 45 deg water you will be comparing apples to oranges! Taylor doesn't really specify a temp at which the tests should be done (to the best of my knowledge) but LaMotte does state that their reagents are formulated to produce accurate results between 70 and 80 degrees.

[DONNIE]

Just for kicks I tested Ph, FC & CC last night both at 41 degrees and a couple of hours later (from a sealled container) at room temperature, aprox 72 degrees. All tests came out exactly the same. I know now not to test CH and TA unless they are at room temp as the results come out completley different that at 41 degrees. I havent tried salt at the two different temps but my test at 41 degrees and my SWG are the same. In the future I will always test at room temperature to get consistent results. Thanks Guys.

Donnie

[waste]

Donnie, you're doing a great job with your new pool and thanks for the input!