Weighing dosing FC by hand vs a peristaltic pump on a timer

Started by Alan Pierce · · 4 replies
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#1
I've been hand dosing liquid chlorine for years, few gallons every couple days depending on what the FC test tells me, and it works fine but it does mean I'm the one paying attention. Been reading about people running a small peristaltic pump off a timer to trickle it in daily instead of one big dose.

The chemistry part I get, a smaller steady dose should keep FC flatter instead of the sawtooth pattern I get now, high after I dose then grinding down before the next one. What I can't work out is whether that actually matters much if your CYA is where it should be, or if it's solving a problem that isn't costing me anything real. Anyone run both ways long enough to notice a difference in algae risk or just chemical usage. Not trying to automate everything, just curious if the flatter curve is worth the setup.

4 Replies

#2
Ran hand dosing for years same as you, sawtooth and all, never had an algae problem from it as long as I didn't let FC bottom out before the next dose. What changed my mind wasn't algae risk, it was that I was buying more chlorine than I needed. Big dose after a hot sunny stretch burns off faster than a steady trickle, UV eats it whichever way but it eats a spike harder than it eats a flat line. Once CYA was dialed in around 30-40 the swings got smaller anyway and I stopped caring as much. If your test strips or kit are showing FC never dropping to zero and staying reasonable between doses, you're not really solving a problem, you're just trading your attention for a pump and tubing that'll need maintenance too. I'd only bother with the peristaltic setup if you're gone a lot or your pool swings hard day to day from bather load or heat. FN
#3
Look, Frank's right about the tubing needing maintenance, that's the part nobody mentions until the check valve gunks up and the pump's dosing air instead of chlorine. If your FC never bottoms out now you're chasing a curve that isn't actually hurting anything, save the peristaltic setup for when you're traveling.
#4
Honestly the sawtooth thing sounds a lot less scary once you know your CYA number, so what's yours actually sitting at right now. If it's in that 30-40 range like Frank's, I'd bet your swings aren't as wild as they feel and you're mostly just annoyed at the routine, not actually losing chlorine efficiency.

For what it's worth my spool is small enough that even a "big dose" is like a cup or two, so the curve barely registers either way, but I could see a peristaltic setup making more sense on a bigger pool with more surface area cooking off chlorine between doses. If your FC test is showing it never crashing to zero before your next dose I'd side with Frank and Dave here, that's a maintenance project solving a problem you don't have.
#5
Look, I'll push back a little on the CYA point Derek's making. Having your stabilizer dialed to 30-40 slows the burn but it doesn't erase the sawtooth, it just makes the teeth smaller. My pool's 18x36 and even with CYA sitting right where it should be I still see FC drop a good ch