Any so called "over unity" generators are a hoax. You'll lose money big time on these every time. These hoaxes come and go all the time. About 10 years ago they ran the same scam in the US. Until they can tap into "vacuum energy" these will continue to be ways to rip people off. You can't get more out than you put in.

While it may be theoretically possible to recover part of the energy you put in from a water turbine from a grow bed, a drop of a couple of feet is quite hard to get anything out of. The cost of the turbine and generator would never pay for the cost. You would be better served putting up a windmill. There are several windmills designed to pump air. You can use this to aerate or even pump water using air powered lift pumps.