Hooking new tank up with 3 year old tank

[Portsmouth Reef]

I have a 280 gallon 8' tank which is running at zero nitrates and has 3 deep sand beds totalling 350 pounds of sand. My 3 year old 90 gallon tank has a canister filter, a hang on fluidised sand bed, and 50 nitrates. I plan to use an overflow box, and run the 90 gallon using the 280 gallon as a sump, then when the nitrates are down, take out the canister filter and the fluidised sand bed.The 2 tanks will then run as one, and have the same r/o top up reservoir. I reckon this will work. Does anyone have any feedback please or foresee any potential problems with this ? I have a well established pod population in the smaller tank, which should benefit the larger tank.

[papagimp]

I took two 75g, one had been running for a few months, the other was "newish". I sumped the two together, split the return line and the only issue I ran into was an outbreak of diatoms. But excess nutrients has always been a slight issue in my setups.