FC dropped overnight


New member
Jun 23, 2017
Fort Worth, TX
Ok so just getting things going. I tested to get some preliminary numbers after initial fill and here they are:

FC - 0
pH - 7.8
TA - 80
CH - 200
CYA - 0 or 30-50 (I haven't added any) but the color on the test strip is hard to tell.
Salt - 1660

As I stated in my introduction post, I blew some sand from the filter into the pool by accident.
There was a big storm that blew off the cover and we lost some water. I filled it back up
and vacuumed. Then I added more salt.

I ran the SWG on boost so that it would run for 8 hours. I checked it after 3hrs and the FC had risen to 1.

FC - 1
pH - 7.8
TA - 120
CH - 200
CYA - 0 or 30-50 (I haven't added any) but the color on the test strip is hard to tell.
Salt - 3420

This morning I checked it and it is back to 0. No change in the other numbers. Any thoughts?
The pool looks a little dirty (got some tree crud in the water at the bottom). I plan on vacuuming it at some point today.

I read somewhere that I need to wait to add CYA until the FC level is up. Is that correct?
Any help on the order I need to do things in would be greatly appreciated. I've read the SWG Water Balance link and some of the other basics.


LifeTime Supporter
Aug 18, 2014
Amelia Island, FL
The SWG is best at maintaining chlorination, but not necessarily intended to tackle the heavy lifting. Use bleach to achieve FC target quickly and SWG to maintain.


Mod Squad
TFP Expert
LifeTime Supporter
Jul 10, 2009
Houston, Texas
I hope you plan to order an FAS/DPD test kit, or at least get an HtH 6 way drop based kit instead of guess strips. Your test results show why we call them guess strips. You say you are getting a 30-50 CYA reading but you have not added CYA. There is no CYA in tap or well water. Unless you have used dichlor or trichlor in your pool there is no CYA.

First, you will need to add enough CYA to reach 70ppm. You do not have to have FC established first, in fact it will be hard to establish FC without CYA. The CYA protects the FC from being depleted from UV rays. Put the CYA in a sock and hang it in front of the return with the pump running. Squeeze the sock periodically to help the CYA dissolve. Use PoolMath to determine how much liquid chlorine to add to reach 5ppm. Input the 70 as your CYA number in poolmath to get started. Keep the SWG running. It should be able to keep up once the CYA has dissolved and the FC has been established.
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