RINSING graduated cylinder before test makes a difference

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Ronald U.

Ronald U.

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May 31, 2015
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Pearland, Texas (near Houston)
I have noticed that when I forget to rinse out the chlorine test graduated cylinder before testing, the FC shows low and the CC high. Then I do a cylinder-rinsed-out-with-pool water chlorine test, and the results show a higher FC and lower CC. Here is today's NO RINSE and then RINSED results:
NO RINSE FC 2.5, CC 1.0
RINSED FC 4.0, CC 0.5

Each time I forget to rinse, the results swing the same way. I suppose CC products build up on the cylinder over the 24 hours it sits in the box. I rinse the cylinder AFTER testing with tap water, and only shake it dry. Thus it is put away moist.

Just thought I'd mention this, as I believe it has led me astray before I realized what was going on.
 
Very interesting! Thanks for sharing and doing the experiment to show your results. When I think back on when I test I notice I do rinse. Did it without really thinking about it I guess.

This is something I will try to mention to new people. Hey I know what! That can be YOUR "job". I would love to see you keeping an eye on the threads and sharing this info when you see it is needed! What do you think???

Kim:kim:
 
Ronald U. said:
I have noticed that when I forget to rinse out the chlorine test graduated cylinder before testing, the FC shows low and the CC high. Then I do a cylinder-rinsed-out-with-pool water chlorine test, and the results show a higher FC and lower CC. Here is today's NO RINSE and then RINSED results:
NO RINSE FC 2.5, CC 1.0
RINSED FC 4.0, CC 0.5

Each time I forget to rinse, the results swing the same way. I suppose CC products build up on the cylinder over the 24 hours it sits in the box. I rinse the cylinder AFTER testing with tap water, and only shake it dry. Thus it is put away moist.

Just thought I'd mention this, as I believe it has led me astray before I realized what was going on.
Click to expand...

I notice you have a Tiger Shark. Will yours climb halfway up the wall? I thought they were supposed to. Mine sometimes will climb, but only when going backward.
 
Yeah, rinse is a BIG deal. It's easy to get a little quick and careless and your results will show it.

Under just plain tap water, I rinse and rinse and rinse some more. Everything....all the time. Often to excess.

I hope I don't sound preachy but dosing carefully, measuring accurately, rinsing always.......all these things fit the philosophy of our Troublefreepool family.

Everything takes just a bit more time and attention but the rewards of having a glass-clear pool just can't be surpassed.
 
And put the tops back on as soon as possible.

When I calibrate, I rinse a few times with the calibration fluid.
 
Absolutely, very important to rinse out the cylinder with sample water prior to testing!

Prior to every test, I fill my cylinder completely with the sample water, then dump it out and fill again to the correct level.

After running each test, dump the test result and rinse the cylinder 2 or 3 times with tap water before moving to the next test.

Each consecutive test gets the same rinse with sample water, test and rinse again.

After completing all my tests I rinse a few times with tap water and then dry the cylinder inside and out with a paper towel. Same procedure with the comparator.

I've worked in a chemical plant for 30 years where test results are crucial for properly maintaining equipment. Our boilers, makeup water and cooling water systems get tested every 2 hours, 24 hours a day 7 days a week. Proper rinsing/testing procedure is one of the very first lessons our lab manager taught every new operator. Rinsing is a habit I doubt I could break even if I tried, lol.
 
I always keep a gallon or so of distilled water around (about $1/gal at your local grocery store) and I use that to rinse and clean my chemistry gear. Folks who keep large aquaria will sometimes have their own RO setups for creating demineralized water which is a great thing to have around too. Since I don't have a water softener (on the list of home upgrades for the future), my tap water is very hard and will leave white water spots all over everything if not rinsed and dried properly. As is true with all things chemistry related, your results are only as good as the care with which you follow the directions and your best attempts to perform the experiments the same way every time - consistency and cleanliness are your friends.

I also say this - there is often at least one or two posts per season by users thinking it a good idea to keep old dropper bottles around in an attempt to reuse them with larger sized reagent stocks. As much as I hate discarding useful stuff, I never reuse old dropper bottles. The reagents are cheap enough in terms of unit cost ($/test) that trying to squeeze some additional cost savings out of it is not really worth the additional effort of storing larger quantities and reusing droppers and there are too many ways to introduce chemistry related errors that way.
 

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My straight tap water has significant CC in it. I believe it's one way the municipality chlorinates the water.

If I dump a completed test with zero CC into the sink with running water, it turns pink immediately.
 
I would suggest that when you first start your tests you always rinse the tube before and between tests with your sample pool water, not tap water. Then, at the end of testing, you can clean everything with tap water.
 
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