Nursery Tank

I cleaned out the soon to be nursery tank today. It was at one point a coral reef tank but hasn't been maintained. This smaller tank is made out of glass and can be carried around so it wasn't difficult to clean.

I'm going to use a small pond pump that I have to get water into it and use gravity to get the water back. I needed to figure out how big of a pipe I will need in order to get the water to flow back into the big tank at the same rate that the pump is filling it up. I found a great book called Aquatic Systems Engineering: Devices and How They Function by P.R. Escobal. It is amazingly helpful in its analysis of life support systems. In this case I opened up to the section on the modified Bernoulli Equation.

I put the pump in my swimming pool and timed how long it took to fill a 5 gallon bucket. The pump flows at 339 gph. For my purposes I did not need to account for head pressure because this gravity return pipe doesn't have a pump. For this I used the following formula:

H_n= H_B + b K G²/d⁴

Where

H_n = water level in nursery tank

H_B = water level in big tank

b = constant = 7.2035x10-7

K = Friction Loss

G = GPH

d = diameter of pipe

I used the following values. K was calculated by this: There will be 6 elbows each worth of friction value of .9 that equals 5.4.

5.5 = 5 + 7.2035x10^-7 x 5.4 x 339.6²/d⁴

d is around .9 inches

Note that I gave only the hight of the nursery tank above the big tank a value of .5 ft, this is a little safe so that the drain will remove water faster than the pump will fill. Also the drain pipe is not going to be a simple U syphon, it will be designed so the water level stays constant no matter what. See the the pic below to get the idea.