Overflow system help

I have an eheim 1262 that's rated for about 900 gph.

1) - How many gph does my external hob overflow box need to be?

2) - What diameter should my feeding and return flexible hose be?

 

The general rule of thumb going around right now is 30-40 times the size of your sump per hour. Dont know what size tank you have but the common size for return in 3/4".

 

The pump is rated at around 900-1000 GPH at 0 feet of head. You need to determine the vertical distance between the water surface of the sump and the top lip of the display or water level if the return is drilled. Its usually like 4+/- feet plus add a couple feet for fittings and line losses in the plumbing so say 6 feet to be safe. Now, what does the 1262 produce at 6 feet of head? You will want an overflow box designed to handle that flow at a minimum and probably 20-25% to be safe so something like a 600-800 GPH overflow is my guess without knowing your system particulars.

The total turnover depends on your corals and inhabitants, hard stony corals like lots of flow while soft corals or fish only prefer lower flows. Its not unusual to have 30-50x the display volume (not the sump volume) in total flow between the return pump and things like powerheads or a closed loop. The return flow itself is usualy best at around 5x the display volume (again not the sump volume) with the rest made up with powerheads etc.

Plumbing or tubing sizes will depend on system size and the GPH you need to produce with as little restriction as possible. For systems up to say 100 gallons +/- a 1" overflow and 3/4" return are very common with smaller systems using more like 3/4" and 1/2" and larger systems using larger diameters or multiple overflows and returns to achieve higher flows.

There are many many articles and sticky post threads in the New to Reefs section further down the forums page. Take your time and read as much as you can before starting to shop, it sucks to make an impulse buy only to discover its not really what you needed.

FYI 30-40 times your sump volume would usually be a microbubble nightmare since the baffles would not function well to dissapate bubbles and your skimmer would not function well, they like much slower flows and contact time. Even the 5x the display volume could be a headache if you have a very small sump. Make your sump as large as you possibly can in relation to the display for best functionality and room for things like return pump sections and pumps, skimmers, reactors, heaters, multiple baffles, refugiums and who knows what else.

 

That should be a 'sticky' post! Agree totally