It's been flowing...Added one bag of instant ocean to sump, almost all dissolved. Bags says is makes 50 gallons, right now reading 1.010 on refractometer. New heater arriving tomorrow, warmer water should help the salt melt. Thinking of letting the rest of the salt in there dissolve overnight, then using wife's blender to make super salty mix, and add slowly to get salinity right. I don't like this sump already. it's too small. I haven't added rock in it yet, just mixing in salt right now. I'm going to custom build a sump to fill the space under the tank before I enclose it, and perhaps a separate refugium next to it since I'm building down the wall some cabinets, stereo stand, MAME game console, etc. The sump might be ok, except the pipes are not glued together inside the overflow box, so if pump goes off, the box leaks down into the sump. So water cannot be very deep. I'm not glueing them now because I'll replace them with bulkhead fittings for pipe instead of hose. With my custom build, the drain can be straight pipe down into sump, no hose.