The Hiblow 5.14ft suggestion operation comes from their website where their optimum operation pressure is 2.57psi (yellow dotted line on their pressure curve chart for HP100&HP120) and from the Hiblow operational suggestion to a Hiblow user.
Bill,
Thanks for clarifying where that came from. What you're calling Optimum Pressure, is what they call their Rated Loading Pressure. As I understand it, that's the back pressure they picked to determine average flow output of that model and to compare data between models. But there is a Curve, ranging from much more, to much less, depending on the load.
The Auto industry also does something like this to compare MPG between models and like the curve in pumps, that MPG is not constant across the board, so there is City MPG and Highway MPG.
The key piece of data on the HiBlow pressure specs is - "Maximum Continuous Operating Pressure = 4.35 PSI". This is what the pump is designed for. At this pressure the Curve chart shows an excess of 3 CFM, which as you know, is very capable of running 3 Diffusers at 8ft depth. I used to run my diffusers at the 11ft bottom for 'maximum effect', but later learned (here) a thermocline is advised for the fish, so it's at 7ft now and is probably what most pond owners should be doing. Importantly, well within the wheelhouse of the HiBlow.
I'm not biased against the Gast pump, I know it's a good pump, but IMO it's just not the best choice for the average cost conscience pond owner.
If I had a very deep pond and didn't care about maintaining any thermocline, I'd consider the Gast. But I'd be reminded of this choice every month, when the electric bill arrives.
When comparing the Gast and HiBlow at 4psi back pressure, I see the Gast is capable of running 5 diffusers, the HiBlow 3 diffusers. I'm not sure the average pond owner (an Acre or less) needs 5 diffusers and Gast takes more than 5 times the energy to run.
