Discrepancy between test kit and pool store results

I have a 3000 gallon SimpleSet pool (the kind with the inflatable ring on top). I use an Intex salt water chlorine generator. Unfortunately, my husband set up the pool before I had salt to put in the water, so I'm fighting an algae problem. It's not terrible...the water is pretty clear, but it has a very slight greenish tint. I've been running the chlorine generator a lot to try to kill the algae, and the water definitely has that "chlorine" smell.

Last year, I bought a Waterpik test kit (contains 5 little bottles of chemicals to perform various tests.) According to that test, my numbers are:
FC: Kit tests up to 3ppm; I diluted 1:7, tested, and multiplied result by 7, giving me about 21ppm.
pH: 7.2
TA: 80

I didn't have any CYA or polyquat, so I headed to the local pool store to get some. I figured I'd have them test my water as well. Their results were VERY different:
FC: 1.9 ppm
TC: 1.0 ppm
pH: 7.2 (aah...we agree!)
Hardness: 70
TA: 0 ppm
CYA: 10 ppm
Copper, Iron: 0

I'm thinking about taking another sample to another pool store...I don't think I'd be smelling all that chlorine if the level was only 1.9, right?

Do I need to increase the hardness based on the type of pool and chlorinating system I have?

Thanks!

Dilution of 7:1 is practically meaningless.....there's just no accuracy. You need a good kit that will test higher levels than 3.

Chlorine smell is an indicator of Combined Chloramines and means you need to add morechlorine/ Shock your pool.

Yes, go to another pool store...their numbers were incorrect.

Disregard hardness.

Best of all, get a test kit so you can get your own results....accurately. Walmart's HTH 5-way tests up to 5ppm and will test CYA as well. It's nothing like Ben's, but it's better than what you have.

I went to the other pool store... their results:

FC: 3 ppm
TC: 3 ppm
pH 7.2 (we all agree!)
CYA: 12
TA: 20
Calcium hardness: 71

Added to my TO DO list: add baking soda, run the chlorine generator for 12 hours tonight, and buy another test kit :)

Thanks for the heads up about the chloramines...I'd wondered about that, but I also thought my chlorine levels were a lot higher than they really are.

So, does this all mean that my current test kit is useless for testing chlorine levels? Or will it be accurate once I finish the whole shock routine and get rid of the chloramine? Does the chloramine somehow affect the test results?

The reason I tried to dilute the sample was that when I did the test on the "pure" pool water, the resulting water color was way past yellow...it was orange. Since the "control" colors that I was to compare it to are all in the light- to very light-yellow color range, I figured that my chlorine level was really high.

Your test kit is not necessarily useless--but understanding that the OTO test kits are not precise to begin with, and you lose a little more accuracy each time you dilute. So a 7:1 dilution really is not accurate enough to act on. Once you get your algae problem cleared up and can let your Cl levels fall back down, the kit will be a lot more useful.

Janet

Godiva,

I would recommend you shock the pool with bleach...not your chlorine generator. .5 gallons of Clorox will bring your Cl up to around 12ppm and should get rid of the chloramines.....the SWG will take too long.

If you'll put in 1 lb of stabilizer, (CYA), your chlorine will last longer and your SWG will not work nearly as hard....extending it's life.:)

I poured a gallon of bleach into the pool last night, and this morning it still had a greenish tint.

I got the WalMart HTH 6-way kit, and I still can't tell what my TC is...when I put the 5 drops of OTO into my water sample, it turns a deep orange color, and then within a minute, bits of orange sort of coagulate and become suspended in the water. :confused:

While I'm working on the levels, do you think it's okay for the kids to go in?

Use one part pool water and one part distilled water. Mix well, test from that, and see if it registers at 5 or less. If so, then read your result and multiply by 2. Again, you're going to lose some accuracy each time you dilute, but without a dpd-fas test, that's the best you can do.

Janet