Oh, and let me tell you one on me: I have an autotopoff on a dual float. I was tired. The darned hose had fallen out of the port and the float had signaled 'need', so it happily pumped 32 g of ro/di water onto the floor. I rammed the hose in good and deep into the port, refilled the ro/di barrel [fortunately I have my own unit] and set up again. For the next while, I couldn't get the salt to stay up---I worked and worked, I used half a container of salt---and it wouldn't stay up. It finally dawned on me: by jamming the hose down INTO the sump, I'd created a siphon between the barrel and the tank, so every few seconds, the siphon would drain water off, the autotopoff would signal 'fill', the barrel pump would cut on til it satisfied the autotopoff unit, and then the back-siphon would drain it back into the barrel: cue the autotopoff; fill; backsiphon...repeat 20-30 times a minute, oh, for a day at least.
I couldn't raise the salinity because I was slowly, step by step, raising the freshwater barrel's salinity to equal that of the tank---a slow process, at half a cup a go. I felt like banging my head against the wall when I realized what had been going on.