Considering a sump

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Aquarium Advice FINatic
Mar 14, 2006
I'm thinking about building a sump to my 75g - tank is glass, not drilled, bottom is tempered.

I'm not really up to the task of draining the tank to drill the sides. Has anyone ever drilled a tank for a side bulkhead, with the tank half-full?

Otherwise, I'm looking at an overflow box.

With a big enough sump (20-30g), I'm not sure how flooding can really happen, if everything is done right.

If there's an overflow box, setting for example 1" below the water's surface - that's abouty 3.75G of water (1/20th of the tank) available to drain out, should the pump fail.

Then, in the sump, if I have the return pump, say, 2" below the surface, in a 20G sump, there'd be around 2G of water available to pump back, then should the siphon fail.

If I give myself an inch of "overhead" above the overflow box's (meaning there's an unused inch or so in the tank), how could the system overflow?

Okay - powerloss could cause the water to drain down to the pump - but again, if the pump return is, say, a little higher than the overflow box, there wouldn't be enough water to flood the sump. Also, a checkvalve would prevent draining to the sump via the return pump anyway (assuming its 100% reliable).

Just seems with a big enough sump, there'd never be any worry of flooding either the tank or the sump - and can't you always set the sump inside a bigger container to catch any spill-over?

I'm trying NOT to rely on the siphon, and not to rely on float valves/checkvalves, for a 100% reliable, flood-proof system.

Does this make sense?
I would not drill the glass due to possible breakage even if not tempered and due to too much water overflowing the sump if your pump stopped.

Good post on a DYI project.

You have the logistics figured out as far as spacing and flooding are concerned. Most overflowing happens because people pump from the bottom of the sump which will overflow the main if the overflow looses siphon.

I’d invest in an auto-top off for the sump since your pump intake is close to the surface of the water. I’ve linked some options below.

Tsunami Top Off System
UltraLife Float Switch
Reef Fanatic Level Controller
AquaHub Top-if-Off Kit Premium
Would a 20G sump be big enough for a 75G tank? Understanding that the bigger issue is overflow of the sump if the pump fails.

Any how do you figure how many bio-balls you need? I'm running fine now with 2 biowheels, so I'd think a gallon of bioballs would be more than enough surface area...

tecwzrd, thanks again for the helpful info.

I'm a little hazy on the top-off setup.- That means you have another container of water which fills the sump should the water level drop? Isn't that a problem if the siphon breaks, and water continues to pump from the sump to the tank? Won't a top-off just keep adding more water and flood the tank?
Scoot said:
Won't a top-off just keep adding more water and flood the tank?
I was more concerned with water going below the pump due to evaporation and forgot about it flooding the main if the siphon broke. Luckily siphons rarely break on overflows IME.

I use a 20 gal filled about 2/3 or about 13 gal full and that has worked out fine for me.

I wouldn’t fill your sump with bio-balls since your bio-wheels should be adequate for bio-filtration. Filling your sump with lr rubble would be more beneficial. A 20 should be enough room for a skimmer and maybe a lighted refugium.

How are your no3 levels doing? Are you planning on adding lr to the main?
I'd like to eliminate the HOB filter with the sump... I figure I'd have to run both for the first month or so.

Without the HOB, wouldn't I need bio-balls, or lots LR of rubble?

no3 is good - PWC yesterday and today (I'm dripping it in, takes about 8 hours for 15 gallons). Almost done with the last few gallons, but last time I checked it was around 10ppm.
Scoot said:
I'm dripping it in, takes about 8 hours for 15 gallons
You are being just a tad too careful. As long as you mix your SW the day before and bring up to the mains temp/sg/ph/alk you do not have to drip the replacement water. I change out 8 gal every week and its pumped back into the tank in about 2 minutes. Just pour it the replacement water back in slowly enough not to disturb the sand and you will be fine.

Bio-Wheels or Bio-Balls both do the same thing and both need to be cleaned often to keep waste from building up. Any filter medium with water moving over it will work for bio-filtration but lr rubble and more specifically lr in the main tank has two advantages.

1. lr in the main with a clean up crew builds up little waste.
2. bacteria deep within lr develops and converts no3 to nitrogen which escapes the tank as gas.

What about adding more lr in the main? You have 13 lbs now, with 70 lbs of base and/or lr you could do away with the HOB or bio-balls.
I've thought about that (adding more LR). I'm up to 20lbs now.

The money works out to be about double the cost of a nice sump (another 50 pounds at $8 per = $400), but long term would be nice.

I've read about that method (the Berlin method?), using all LR for filtration. Then just run a protein skimmer?

The LR I have now is "branch" type (see the most recent pic in my photo gallery), and is taking up some room. I'll have to find more solid style rock to get another 50 pounds in there.

There is a real nice, big piece at a LFS. Thinking about getting it, its 30+ pounds (30x$8=$240). All the rest in the area is either rubble or branches.
Long term lr is worth the money not only for hassle free bio-filtration that you don’t need to clean every week but also as a natural home for your fish/inverts. I’ve got 90lbs in my 55 gal and it’s pretty full but I could still add about 20-30 more. I think you could easily kick it up to 90+ lbs in your 75 gal. Just need to rearrange your rock a little bit.

“Berlin method” has been used for decades. 1.5+lbs per gal and a quality skimmer is all you need. Have you checked out They will ship 50 lbs to your door for $167.50 or 75 lbs to the airport for $243.75
I'll get there eventually. I'm sure it'd look great too, and the fish would love it.

Meanwhile, I picked up some things for a sump. 20g long tank, some pre-filter material, and tomorrow I'll go get some plexi cut for two baffles and a lid over the bio-ball area. I've got a winning bid on a nice 300gph overflow box with lifter pump, just need some eggcrate to hold up the balls, and a pump (Mag 5 I think is what I'll go with). Total cost, before the 3 panes of plexi should be around $80 to $90.

I think I'm going to talk the SO into that big piece at the LFS.
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