CC in fill water

[Terry]

<<Many cities, including my own, use CC instead of FC for chlorination because it lasts longer in the pipes so when added to the pool this uses up some of the FC although it should be proportional to the amount of fill water added each day. You might want to test your fill water for CC just to see.>> I pulled this comment off: ugh-pass-the-pop-t58914.html

I am having a hard time getting any measurable increase in chlorine even with the addition of enough dichlor to raise it to 3.0. New pool, plastered Wed, finished filling Fri morning.

Tap water FC: .5 CC: 1.5 I assume this means the city is treating with monochloramine. I also think I understand that getting rid of the monochloramine is taking a larger chlorine demand? Is there a table/ ratio that tells me how much chlorine it will take to wipe out the monochlorine? With the new plaster I'm hesitant to add more than needed.

 

[257WbyMag]

I would imagine that you are losing your chlorine in rather short order because your CYA is low. Adding enough dichlor to get your 20K gallon pool to a FC of 3 will only raise your CYA to 2.8 or so. You need at least enough CYA in there to get you to 30.

 

[JasonLion]

With plaster in the first week you are best off only adding 1 or 2 ppm of chlorine at a time. With fresh plaster you also generally run the pump 24/7 for the first while. Assuming you are doing that already, the simplest thing to do is to put two trichlor tablets (one for each 10,000 gallons) in the skimmer(s) and let them take care of it. Trichlor will raise the FC level very slowly and gently and take care of the CC level in the process over the next several days.

 

[Terry]

Thank you. I am running trichlor in a tablet floater, and added the dichlor (predissolved in two 8oz additions) to attempt a burnoff of the cc. Since I did the bicarb start-up I intend to use the trichlor for the first month, letting the CYA rise over the month. I am running 24/7.

I was concerned the monochloramines were consuming my chlorine, leaving me little for algae control. If I understand correctly, I needn't worry about that. Thanks again!

 

[257WbyMag]

The monochloramines in municipal fill water don't have much effect on the consumption of your FC. Your FC loss is more likely due to sunlight at this point.

 

[chem geek]

Ideally, it takes half the CC amount as FC to oxidize it though in practice it's somewhat more than that so a simple rule of thumb is 1:1. In pools maintaining FC/CYA ratios at the minimum recommended on this forum for non-SWG pools, it takes about 7 hours to oxidize 90% of it and 14 hours to oxidize 99% of it.

 

[Terry]

hmmm, well I can't seem to get the Cl level up to the minimum, the best I've been able to do is a weak .5 on the FAS-DPD so I suspect it's probably closer to half that. I did, however, get a CC reading this evening of 1.0 so I suppose it is slowly oxidizing it. I just don't want algae to get started as I don't want to have to up the Cl to combat it. The water is still clear so I'll ride it out and hope for the best.

 

[JasonLion]

That is because your CYA level is really really low. Because CYA is so low, your FC level is actually fine. Just make sure you have two trichlor tablets in the skimmer and the pump running 24/7 and FC will be fine for the first couple of weeks.