Is it normal to need more chlorine every day? Is it safe for chlorine to drop to 0?


New member
May 30, 2020
South Jersey
My pool looks great other than leaves that are still dropping from the tree behind it. I opened it last week. At first, it was clear but had some grey muck on the liner and a few leaves that had fallen in over the winter. I shocked it at night with 5 gallons of liquid chlorine (12.5%) and the next day it was clear and blue. Maybe 5gals was overkill, but I was concerned about the grey on my liner.

2 days later I had the pool store test my water. (I'm getting a TF-100 & smart stir soon). My first test results were 0 CYA, 40 alkalinity, 7.2 pH, 0 calcium, and 0 total/tree Chlorine. I realize the chlorine burnt off because the CYA was too low. I back-washed and then slowly added 3lbs of stabilizer to the skimmer (will use a sock going forward) to boost my CYA. Then I added around 64oz of LC (12.5%) last night based on the Pool Math advice (cool app). The filter has been running and I'm bubbling the return to raise the pH. I put in around 1lb of washing soda this morning to raise my PH and Alkalinity. I don't think I need to worry about the calcium.

I'm going back today to get new numbers from the store. I'm shooting for 3 FC, 7.6pH, 70 TA, 0 CH, & 30/40 CYA.

Anyway, to make a long story longer, I've found in the past that my FC will often go to 0 the day after I've added a maintenance dose (~64oz). Is this normal/safe? I heard it's very bad and maybe unsafe to let it get to 0. The pool store keeps pushing tablets to prevent the 0 FC reading and telling me that liquid chlorine will wreck my liner. However, as long as I'm slowly topping it off each night (with recommendations from Pool Math), should I be concerned at all if my FC tests at 0 by the middle of the next day? Is it normal?

Thanks in advance,


Gold Supporter
TFP Guide
Jun 8, 2019
Milwaukee, WI
Dave - you heard right that 0 FC is not good. It means algae and bacteria can grow. You don’t want that.

Sadly we’ve had too many issues with giving advice on pool store tests, so we can’t give specific advice until your kit comes in and you can do your own test. In the meanwhile, add 5ppm worth of liquid chlorine daily by slowly pouring it in at a return jet. (Pencil-sized stream as you pour.) It’s perfectly fine on the vinyl so long as it mixes in right away and you don’t get too high with the FC compared to your CYA.

When your kit comes in run the tests and give us the numbers :)
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