How many GPH out of 3/4'' drain

What size tank is it? How big are your return lines?

The drain lines are usually larger than 3/4", expecially if the tank is large enough for 2 overflows. Since your drain line is the larger of the two holes, the drain lines will be able to handle more water than your return lines. So, the amount that drains is determined by the amount that is being pumped back into the tank.
 
For the 3/4", I assume you are referring to the inside diameter of the line. To calculate the drain rate, you need to measure the distance from the water level to the middle of the drain pipe or opening if you have a standard overflow box. Here are some common drain rates in gallons per minute based on typically distances:

1/2" - 1.8
1" - 2.6
2" - 3.7
3" - 4.5
6" - 6.4

So if you have an overflow box with 2" water level above the pipe opening, you would get about 222 gallons / hour drain rate. (3.7 x 60)...

These calculations can be found in "The Reef Aquarium" by Delbeek & Sprung..
 
I would say.... not enough. On a 75 Gal I would go with a pair of 1" drains.
remember; if you go with a union, it will actually reduce the diameter by about an 1/8th inch
 
You must log in or register to reply here.
Top