Jenja

Biggest question I'd say is what's the room temperature where it's located. So long as the ambient temperature is high enough I'd avoid a heater in such a small volume of water. I'd also plan to have a couple gallon jugs prepped in advance so that they are the same temperature for your replacement water from the turkey baster waste removal. As for the filter, I'd either run it or a small sponge, simply to avoid stagnation.

Growing up my home had a water purifier (aka softener) and I never truly understood why I struggled with both plants and guppies - nobody in the lfs ever pointed out that it was stripping the GH (my impression was it was about the high iron content in our well water). Unless you are plantless and/or keeping soft water species then you're going to need to increase your GH. Most say that there's an at least one tap unconnected to the softener, or a way to bypass it - I'd probably try asking whoever installed it about bypassing it. If not the simple way would be to test an outside tap's water and see if you have one outputting the high GH water. Personally I'd probably go for equilibrium (I do now). I can control the GH and it is helpful to the plants (some potassium in it if I remember correctly). As for salt in the water? The salt solution recharges the resin that is taking out the calcium via ionic exchange - it's not flowing into the water supply (unless I imagine you are attempting to run water during its recharge cycles, but typically those are programmed for late at night - ours happens at 2am til approx. 4:30am every few days). I've been tempted to purchase a saltwater refractomenter (I think that's the name of the tool that measures salt in water) to confirm but never have, operating under the theory of if there was salt in the water that I'd taste it if it were enough to be harmful to my plants/fish.

My endlers tended to be slow to go for repashy (community blend and grub pie variety). Typically taking 5-10 minutes before they realised it was food sitting on the bottom and finally swarmed it. This made me wonder how I could suspend it near the surface for them. My solution? Mini fishing bobbers. I thankfully had a magnet wand hanging around, making dipping the bobbers much cleaner - simple dunk in the repashy, then dunk in cold water, and gently break the magnetic hold onto a paper towel. The odd dunking will occasionally fail (typically when the repashy has cooled too much and needs to be re-microwaved) but otherwise it holds in the tank will provide me with a good half hour worth of entertainment as they swarm it around. Three things I've learned using it; 1. Small batch is best for the number of fish I have (1 tablespoon repashy, 2 tablespoon water). Lasts for the two weeks without needing to freeze. 2. My ratio can be done in a silicon portion cup, making it easy to heat and reheat. It also can be poured onto a piece of parchment paper to set quickly - less than 5 minutes to make and have sliced and in the fridge. 3. You don't actually need boiling water. So long as you microwave it until you see it bubble up (less than 30 seconds in mine), it sets just fine with starting from room temperature water. A secondary boon with that? The smell is greatly reduced - no more waiting hours for the smell to dissipate.