Backyard Aquaponics
A place to discuss aquaponics

That would make life simple, but I don't have a sump so the only place to put the float valve is in the FT. Using city water would sure make life easy, but I'm worried about the water direct into the FT, especially if there's a problem that lowers the water level more than normal.

My current plans include a float valve supplied by my rain barrels, but they are rarely full in the summer, so I though about topping an IBC with city water, either aerating for 2-3 days or treating with Prime, then a pump on a timer will kick in twice a week to supply the float valve with blended rainwater / treated water.

But that's a pump, timer, some float switches and automated valves to add. Connecting the tap to a float valve will be soo easy, but I've seen a few worst-case scenarios and I can see a plugged drain / overflow or broken pipe or something draining my system and the float valve providing all the tap water needed to keep it topped up, killing fish and bacteria.

The risk is low, but the consequences are extreme.

the only real option is to have something like a rainwater tank with a bit of volume.
2nd hand under-eave type 1000-2000L ones common in Aust but don't know about for you guys.

Anything complex always involves risk, so other option is just to use an irrigation soleniod & timer and release a certain amount of water every couple days and run the system with a bit of capacity. It wouldn't be perfect but it would allow for some automation and could be changed quite easily to suit seasons.

If you have a top-up switch and something goes wrong somewhere else in system you just end up draining your system and your backup supply.

Hmmm, irrigation valve. Good call for tap water supply - it has the pressure to drive that, and I could just make it part of my sprinkler timer program.

I do have a rainwater catch system that used to include a 1000l and a 1250l IBCs, but they were re-purposed (temporarily) for my juvenile catfish and large tilapia. But after the juvenile cats are big enough to swim with the big boys and not get eaten, then I'll get my 1000l back, and after I eat the tilapia (30?) the 1250l.