I myself would run it from one larger return pump that is split and have just one overflow per tank, but that is much a muchness. I prefer to have the movement in the tank mostly generated by powerheads in thet ank and not by the pump which is always leaching energy fighting the head pressure. Others prefer not having any pumps in the display aquarium.your best option would be to have one sump feeding the 2 tanks,
with 2 over flows from each tank and 2 return pumps,
but be aware of the risk of cross contamination, if one fish gets sick in one tank it will spread
The way you are doing it is the quick way to a wet carpet. You can't just put a pump in each one and pump water across. One pump will always be a little bit faster than the other and then you will get an imbalance. The way to share without a sump tank would be to create a syphon (like with the water bridges in the DIY/Hardware section) or to drill each tank and connect them with a pipe (as I have done with the two sump tanks on my 6x2x2).basically I am running ozone and a vectron uv25 which will easily cope with 2 x 240 litre tanks;
I have to eheim pumps currently that i have configured to pump water back and forth after 3 hours of running the levels are uneven
I would be happy if i could get this to work on a day basis. and adjust the water levels accordingy. I understand the risk of cross - contamination. If I am exchanging water with the two pumps, i currently have two external filter set up on each tank. will this make the good bacteria from one filter go into the other through water transfer