I like Masterblend or
Prochem's descale juice
I descale the solution lines too
I do it two ways, either by simply pouring the juice in my water box then turn the pump on and after a minute or two, I'll put the end of the sol line into the water box and let the acid recirculate. for a few minutes under temp, then shut it down for 10 maybe 15 minutes, then flush everything with clean water, then a bit of emulsifier.
or if I don't feel like cleaning/rinsing the water box out when done, I have a hose made up that plugs into the the line the pump draws from.
(my TM has QDs on all the TM plumbing)
I just let if suck from a 5 gal bucket of descale solution.
Let dwell for time, then flush/rinse
Do the sol lines too
..L.T.A.