Somehow my brain saw 8.5... 3.5 is a bit high.
Sent from mobile device. Beware of brevity and spelling errors!
Oh yes, I remember the 31.2. Just whenever you don't plan to check FC for 24+ hours.
Just a quick hello and welcome. Our "new to us" 325 gallon Hot Springs now literally takes 2 oz of bleach each use and 1/2 oz acid every couple of days. Its SO EASY. I test frequently for fun...not cause I'm worried. Our spa and pool are easier and cheaper than at any point since we've owned em. Trust the advice you get here...trust PoolMath...and "listen" to your water. You'll quickly discover it "tells you" what it needs. Don't overthink. You're biggest problem will be the wrinkles on your skin from enjoying your spa!
What's your water temp currently at? 5 ppm loss over 12 hours is certainly a bit high and the 1 ppm CC is concerning. Is the spa cover on at all times when not in use? Getting a little sunlight on the spa in the afternoon can help burn off some residual CCs. At this point, it looks like you're doing everything right. Maybe a little more detail will help.
I just saw this thread, and it brings back memories. I have a Marquis spa I bought in 2008, and it has the spa frog cartridges for minerals and bromine. I have never been happy with them. Too hard to calibrate. Never was right. Water would be good after a change for a short while, and then just not great. I too had that brown scum at the waterline when new. Never sure what it was! Fast forward to this year, and I have changed to the dichlor/bleach method. Absolutely terrific. Water is perfect, and I understand the chemistry. I have a TF-100 test kit for the pool, and I use it for the spa also. So, you made a good choice getting rid of the cartridges and going with the chlorine. Much better.
Thank you all for such a useful thread. we've been using frog cartridges and adding Spa Essentials Brominating Concentrate for almost two years now, and I'm just not happy with the water. We added an ozonator last year and I'm still not happy.
It's not so much that the water has ever changed, I think it's just that our standards have risen a lot since my wife went full TFP with our pool last summer. We just changed the water in the tub and I'm once again getting smacked with how unhappy I am with the bromine, so I'm looking at changing over to chlorine at the next change. More reading for me, I guess.
I probably need to mention this over in Complaint on TFPC Method.