I would be inclined to think that the Hydra's high frequency, high current switching is causing significant induced coupling to the heater's ground conductor and coupling that to the water through the heater's grounded envelope, or even placing actual leakage current on the ground.
In either case, I would want to make sure that the wall receptacle's ground and those of the power strips is functioning properly. This is easier said than done and therefore the best course of action is to run all of the equipment through a GFCI. This will allow the GFCI to break the circuit if that "tingle" is actual fault or leakage current.
I would leave the heaters on the second power strip, away from the HYDRAS.
I would consider adding a titanium ground probe, noting that this may be what the heater are doing, but the resistance in the chain heater shell --> wire --> power strip --> receptacle --> earth is higher than from your finger to ground.
Let me be clear about the grounded titanium heaters and/or the ground probe. In either case the path to ground is dangerous without a GFCI protecting the equipment plugged into the tank. It creates a scenario where you can become the circuit between a fault and the grounded water, even wearing insulated shoes for example. GFCIS are not optional here.
I would buy and use a simple receptacle testers that shows miswire and missing ground.
There is a lot more here that could be related to using two different receptacles and/or circuits connected to the same tank causing ground loops, but the combination of GFCI and properly testing the receptacles and electrical strips will eliminate most dangers.
I want to touch on the two circuits scenario. If those two different receptacles on opposite sides of the room are two completely different circuits (or even the same circuit with significant difference in wire length or bad connections or receptacles): Any slight difference in electrical potential or ground resistance between those two circuits will use your highly conductive saltwater to try and balance itself out. This (again) is why GFCI protection is so important.
I am sorry that my answer sounds generic, but there is a lot that would need to be tested through a fairly complicated process of elimination to actually figure out what the culprit is. In the end if it is annoying induced current, the GFCIs will not trip, and if there is dangerous fault current they will.