I'm in St Petersburg, Fl, and am converting my above ground 15'x26'x52" 11,000gal pool from Baquacil to chlorine - something I should have done YEARS ago! The question I have is whether it's really necessary to change out 150 lbs of sand from the 22"filter - some background :
Pool was last used last Nov. and pool store computer testing last week showed 20 ppm of sanitizer left; pH, CH, & TA all OK. After cleaning out all the leaf debris and vacuuming the floor so that all was clean, the water was kinda cloudy from sitting partially covered all winter (adjacent deck leaves a gap for the MANY leaves to fall through), but mostly clear. I'd read all the posts about color changes & having to backwash "baqua goo" from the sand filter for days, or even weeks, after adding the bleach, but what I actually experienced was the water turning an aqua color (could still see the bottom liner) and less than 24 hrs later, it was sparkling clear. I did go through lots of chlorine during the first day maintaining a 15 ppm FC level but only backwashed once, which didn't look all that bad. Had out of town visitors (a curse all Floridians endure about this time every year from our northern family and friends!), so wasn't able to monitor FC late night/early morning, but added bleach every evening (after we swam!)to bring FC back up from next to nothing to 15ppm after sitting in the sun all afternoon. Finally was able to check last night & this morning, no overnight drop in FC, so I'm ready to move on with the CYA & install my newly purchased SWG, but really wonder why I should change out the sand which I just put in last July - I normally changed it every 1 &1/2 seasons. When I backwash now to release rainwater, all looks clear & good - no signs of "baqua goo". In fact, the pool looks better than it ever has!
I'm guessing that since the conversion went so quickly and the sand filter looks so clean, there really wasn't 20 ppm baquacil that the pool store test indicated? And, changing the sand is a major pain in the neck, so I really hate to change sand that's less than a year old.
Whatcha think?

Welcome to TFP!

You might want to open up the filter and have a look at the sand before you decide. What we usually see after a conversion is lots of sort of rubbery goo though out the sand, which significantly reduces the filtering efficiency of the filter and tends to create extra CC. If you have anything like that, you will want to change the sand. If the sand looks pristine and CC is usually zero, then you got lucky.

Many thanks for the quick reply - very impressive!
Doing a visual sounds like a reasonable - and prudent - step to take before adding the CYA, SWG, and moving on.
FYI: I purchased and have been using the TF-100 Test Kit and have found "Jason's pool calculator" to be extremely accurate for maintaining FC levels...... if you're that Jason, thanks for posting it.

You are welcome!

I was the original author of the Pool Calculator. However, the Pool calculator is now owned and maintained by PSI Flow Technology.

OK - pulled off the top valve assy from the sand filter and the sand (which was just put in last July) did look very clean & pristine EXCEPT it had very small, thin grey colored slivers mixed in it which I haven't previously seen. Figured I might as well and just replace it since I was 1/2 way there by removing the top and 150 lbs of sand and another hour's labor isn't a very costly investment of time or money for the peace of mind it ensured.
Added the CYA and am monitoring the chemical balance in anticipation of installing the SWG later this week.
Pool looks GREAT!!!!!!!!! Kicking myself for not switching from Baqua years ago.............. figure to save both tons of $ and time this year

Congratulations!