Only one possibility left: 1. a sea water mineral buildup in your toilet discharge line that's serious enough to restrict the flow....I've seen it reduce the diameter of a 1.5" hose to <.5". It's more of a problem in warm waters than in cold...and you're in FL where the waters are warm.
No-Flex will dissolve sludge, but it's not a de-scaler. There's a product called Sew Clean Sew Clean
that is, but it's considerably more expensive than muriatic acid, which is a available from any big box or hardware
store. Flush a 12-15% solution through to the tank...wait 45-60 minutes, then follow with a couple of gallons of clean water. Repeat if necessary. READ AND FOLLOW
ALL DIRECTIONS FOR SAFE HANDLING MURIATIC ACID!!!
Once you get the hose cleaned out, a cupful--2 at most--of undiluted distilled white vinegar flushed all the way through the system once a week will prevent--
but won't cure--sea water mineral buildup in hoses. Follow the vinegar with clean water after 45 minutes...NEVER leave it sitting in the bowl. Soft rubber--i.e. joker valves--left to sit and soak in vinegar will swell and distort.
There is one more thing worth checking: low voltage to a toilet is the most common cause of sluggish discharge. While it doesn't sound from your description that this is your problem (or one of your problems), you have nothing to lose by checking it. Put a volt meter on the connection WHILE FLUSHING
...if it's getting less than the full 12v, that could be at least part of your problem.
If none of the above solves the problem, it's time to talk to Raritan. The A5 is an obsolete version of the Atlantes that may be old enough to have an age-related quirk that a relatively inexpensive part might fix. 800-352-5630 Talk to Mac McCoy...he's been with Raritan long enough to know the A5...he's my go-to guy. His extension is 306.