No Chlorine Reading

[meggiesmum]

Hi

I'm a new 500 gallon hot tub user so apologies for any naive questions.

I've been using chlorine troclosene sodique dihydrate (french name as live in france), in granule form. Since last Tuesday have added 2 tsp per day and have not as yet had any chlorine readings on my test strips. Have checked test strips by dipping in glass of tap water with sml amount of chlorine added to see if any results show - all ok.

To start the Ph was a little high so regulated that first before adding any chlorine. Total Alkalinity Ok. The water is not cloudy, quite a lot of foam, but according to hot tub supplier this is normal with new hot tubs. Have noticed today a brown/black substance around the water level on the hot tub - tannin???

How long after adding chlorine do I test water?

Any thoughts and comments appreciated.

Regards and thanks

[chem geek]

According to this link, the product you mentioned is just a synonym for the normal dihydrate form of Dichlor (the dihydrate form is much more common as it is less reactive in its dry form -- less flammable, etc. so is in a safer "class" rating of oxidizer).

2 teaspoons of Dichlor in 500 gallons will only raise the FC level by 2.8 ppm. Typical chlorine usage or loss per day is up to 4 ppm FC, but if you try meassuring the chlorine level shortly after adding it, then there is a problem. It's possible you've got some chlorine demand in your water so you need to shock it with chlorine first. If monochloramine is being used by your water utility for sanitation, then it will take some amount of chlorine to use that up. Do NOT use the Dichlor product for shock. Instead, get some unscented bleach (Clorox Regular is good, if that's available to you -- for off-brand bleach the Ultra brands are stronger) and 3 fluid ounces will roughly give you that same 4 ppm FC and you could shock to 10 ppm to start with and see if any sticks around.

Also, after you've got some measurable chlorine residual, use the Dichlor for a week or two and then switch to unscented bleach. That will keep the Cyanuric Acid (CYA) concentration stable as Dichlor just increases it. If you were to use only Dichlor, then the increasing CYA would lead to lower disinfection rates from the chlorine.

Note that test strips are not very accurate (with a few exceptions of the Borate and salt tests) and if you can find it I recommend the Taylor K-2006 test kit (or see if you can get the TF-100 tftestkits.com shipped to you, but I doubt it if you are in Europe).

As for foam, you should measure the Calcium Hardness and if it's low, then increasing it (by adding Calcium Chloride) to 100-150 ppm should help reduce the foaming.

I'm not sure about the brown/black substance, but perhaps that's something that is consuming chlorine rapidly so maybe the shock will take care of it. Could be some left over grease in the new hot tub or something like that.

If the pump is on and especially if you've got your jets running, then testing the chlorine level 10 minutes after you've added it should measure accurately. In a hot tub it doesn't take very long for the water to get mixed thoroughly. Even in a pool with decent circulation, much of the water is mixed in 20-30 minutes (I've done tests with dye and chlorine measurements).

Richard

[meggiesmum]

Thanks Richard most appreciated.