UV treater and chlorine levels

[Briankf]

I have question in regards to chlorine levels when using a UV treater. The pool store told me I could cut my free chlorine in half when using a UV treater. I haven't found anything on the TFP website about this and Pool Math page has no allowance for this.
My tests this morning show:
FC 3.8
CC 1
PH 7.6
TA 260
CH 180
CYA 75
Water temp 80

Is it ok to run my pool at this FC level combined with my UV treatment? This is my first season using TFC method and I've saved the cost of the test kit in startup chemical costs alone!

 

[Donldson]

Well, quite simply no. While a UV system could be useful in an indoor pool, heavily used commercial pool, or a hot tub, they have little to no use in an outdoor residential pool. The sunlight your pool gets has plenty of UV for a pool.

As for needing less FC with a UV system, nope. You don't find anything on PoolMath because even with a UV system you still need to maintain a proper FC level. In fact the UV system is breaking down FC as it runs through, increasing your FC loss slightly.

So bring your FC up to the recommended level for your CYA and stay out of the pool stores. On a related note, your CYA is a bit high. What are you using to chlorinate your pool?

 

[Patrick_B]

Welcome to the forum, and congrats on taking over your pool.

If you run low FC in the pool, you have a chance of pathogens out in the bulk water not being killed. This is largely why we don't suggest UV for residential outdoor pools. It's really not needed either as Donldson says. That you can run low FC because of the UV, we don't agree with that. Too risky IMO.

 

[tim5055]

Welcome to TFP

I guess I'm adding to what the others have said.

UV systems have a place in the pool industry, just not in an outdoor residential pool for the reasons listed above. I would even go so far as to recommend discontinuing the use of it because the minor benefits are outweighed by the fact that the UV system is lowering your FC.