RO topoff & TDS creep

[Dave C]

I've had my RO unit going directly to my sump through a solenoid/float switch thingy. It works great. But the tds out of my RO unit is brutal with so much start/stop etc. If I go & test it at any time it's about 50ppm. If I let it run for a bit it gets down to 0. But with an automatic topoff it will always be cycling for very short periods so the average tds out of the RO will suck. It won't be good for the membrane in the long run either. I know some people use other methods & would like to hear what you're doing. This won't be an issue when I get my larger tank going as I'll use a low & high water float so the RO will start supplying water when the level gets about 2" below normal and will cut off when it gets back to normal. But for the 65g tank there is no controller. Ideas?