I have not started building the Griggs yet but have been contemplating what size to use. I'm assuming 2" but trying to determine how tall it needs to be. I'm only running a 45g and I don't anticipate ever increasing the tank to more than maybe 60g. Having said that, I use a Fluval 406 and wonder about two things. First, with the 406 am I limited to how tall O cam make the Griggs? I was thinking about 20". Secondly, where should I let locate the Griggs after completion? The 406 sits on the floor. Should I also rest the Griggs on the floor? I don't know if raising the Griggs will reduce head pressure and increase flow. If I did raise the Griggs, the outflow of the 406 would have to first go up to the top of the Griggs and then out the bottom and up another 20" or so.
If the Griggs sat upright next to the 406, the outflow of the 406 would be about level to the Griggs inlet but then it must travel from the ground up about 48". This is well under the 7 ft 6" max head but I'm guessing that when it states max head of 7'6", that means that the flow is reduced as the height increases until at 7'6" there is literally no flow. Just speculating.
Does anyone have their 406 off the floor to help with head pressure? I so wish now that I had bought the FX6. And I have even started thinking yet about adding an inline heater! 😧