Noob with some sump and plumbing questions

[Rham1281]

Hi!
I am new to salt water tanks and I have just recently gotten a 75g display tank with a 29g sump. My tank is not drilled yet (that is something that I will be doing soon).

My biggest question is do I need to match the GPH being drained and the GPH of the return pump? I know that I shouldn't have the return rate exceed the drain rate but do they need to be the same?

Also, looking at overflow boxes, I am going to retrofit one after I drill my tank. What are your suggestions for what to look out for?


Thanks for the read!

 

[DCR]

At least one of the drains is designed to work as an overflow so that the drain flow will always equal the return flow unless you undersize your overflow in which case you will overflow your tank or empty your sump whichever occurs first. A properly sized overflow will always drain just what the return supplies to the tank.

I like the overflow boxes by Modular Marine, Exotic Marine or Fiji Cube because the external box can be mounted up high over the plastic rim. Some of the less expensive boxes have the external box below the rim which causes a waterfall in the internal box and added noise. Modular Marine and I think Fiji Cube make the internal box with vertical teeth while Exotic Marine uses horizontal slots. The slots probably do a better job of skimming the surface of the water and have higher capacity, but it is easier for fish to get through the slots and into the overflows. I have Exotic Marine overflows on two of my tanks and I often have to recover newly introduced missing fish from the external box. Both are quality built. For a 75 gallon I would look for one that is at least 20-24" wide - some people really like long ones for skimming (36") but this limits the area for returns and power heads on a 4 ft 75 gallon

 

[Rham1281]

At least one of the drains is designed to work as an overflow so that the drain flow will always equal the return flow unless you undersize your overflow in which case you will overflow your tank or empty your sump whichever occurs first. A properly sized overflow will always drain just what the return supplies to the tank.

I like the overflow boxes by Modular Marine, Exotic Marine or Fiji Cube because the external box can be mounted up high over the plastic rim. Some of the less expensive boxes have the external box below the rim which causes a waterfall in the internal box and added noise. Modular Marine and I think Fiji Cube make the internal box with vertical teeth while Exotic Marine uses horizontal slots. The slots probably do a better job of skimming the surface of the water and have higher capacity, but it is easier for fish to get through the slots and into the overflows. I have Exotic Marine overflows on two of my tanks and I often have to recover newly introduced missing fish from the external box. Both are quality built. For a 75 gallon I would look for one that is at least 20-24" wide - some people really like long ones for skimming (36") but this limits the area for returns and power heads on a 4 ft 75 gallon

So as long as my return pump doesn't go over the overflow's GPH I'll be fine then?

 

[DCR]

Correct, you cannot really oversize an overflow. I do think the GPH of some of these overflows are a bit overstated, but I would be surprised if you ran into that on a 75 gallon. I don't know that I have ever heard of anyone having too small of an overflow. Certainly, if you stay with my recommendation of 20-24" you will be fine. Mass produced tanks come with corner overflows that are much smaller than this and they work. At worst, you may have to turn your return pump down (if DC) or throttle the discharge to reduce the flow rate.

 

[Rham1281]

Correct, you cannot really oversize an overflow. I do think the GPH of some of these overflows are a bit overstated, but I would be surprised if you ran into that on a 75 gallon. I don't know that I have ever heard of anyone having too small of an overflow. Certainly, if you stay with my recommendation of 20-24" you will be fine. Mass produced tanks come with corner overflows that are much smaller than this and they work. At worst, you may have to turn your return pump down (if DC) or throttle the discharge to reduce the flow rate.

Thanks so much for the clarification. That helps me a ton!