90 gal Freshwater sump set up advice

I've never seen a sump that wasn't divided, even on freshwater. I imagine that's because the division allows the water flow to not disturb the substrate, which was heavily planted with fast growers to help with nitrate removal, and had another division going to the return. I don't know how many bioballs you're talking about having, nor do I know how much space you'd have for them if you get dividers installed. I've seen other forums that had pictures of freshwater sumps, but they're much less common than saltwater sumps.

As for canister filtration, I'd recommend a filter that's rated for at least as much volume as you'll have. For you, that would be a canister rated for 125 gallons or better as a minimum. Now, be warned that this means they can get pricy. Sun Sun HW 304/AquaTop CF500 I think are both rated (basically the same filter from the same parent plant with minor cosmetic differences) for 125 gallon tanks, and they're in the neighborhood of $130, I think, because it's considered a "cheaper" brand. On my 55 gallon freshwater I have an AC 70 HOB (upgrading it to an AC 110 at some point in the future) and an AquaTop CF400UV, rated for approximately 70 and 90 gallon tanks, each, if I recall correctly.

For what it's worth, I think a 29 may be bit unsuitable for a sump for a 90 gallon tank. There's quite a bit of debate and many differing opinions, but the general consensus seems to be that a sump needs to be 50% of the volume of the tank or better. In the case of the 29, it would seem you would want additional filtration, because even with the wonderful biological filtration capabilities of a sump, it can only filter so much water at a time.

canister filters only hold a couple gallons and even thought they have a higher flow rate for their size vs a sump, 29 gallons filled with media will be much better that a canister. I don't see why you would need a sum 50% the volume of a tank when 1 or 2 canisters can filter the same size tank at less than 10% of the volume. A sump with a strong pump and overflow is going to be much better than a canister and cheaper if you already have most of the parts. Like mentioned above you can even plant a sump to get rid of nitrates if your fish eat moat plants in the tank.

I don't have experience with a sump but having it divided should improve its filtering abilities by guiding the water through all of the media more effectively than simply flowing over the top of it.

Your sump has to be divided in order to get the water to flow through the media. Bio balls floating on the top of the water will not do anything at all to clean your water.


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poppycock. The balls will be exposed to the water and the air, and moving around. This means there's ample access to everything the bacteria need to survive. The water will move through the system at the same speed--what having them float will do is reduce the number that can be in contact with the water at any given time. Easily remedied by bagging them up, and adding some ceramic cylinders to keep the bag from floating.

One reason to divide a sump is top prevent bubbles from getting into the pump. Without that the incoming water create bubbles, and they go in to the return and create microbubbles in your tank.

ManEatingShrimp said:

canister filters only hold a couple gallons and even thought they have a higher flow rate for their size vs a sump, 29 gallons filled with media will be much better that a canister. I don't see why you would need a sum 50% the volume of a tank when 1 or 2 canisters can filter the same size tank at less than 10% of the volume. A sump with a strong pump and overflow is going to be much better than a canister and cheaper if you already have most of the parts. Like mentioned above you can even plant a sump to get rid of nitrates if your fish eat moat plants in the tank.

I don't have experience with a sump but having it divided should improve its filtering abilities by guiding the water through all of the media more effectively than simply flowing over the top of it.

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You don't fill the sump entirely with media. If you research sumps, the vast majority of recommendations are sumps approximately half the size of the display tank. Some are as small as a quarter of the display, some are as large as the display. The amount of flow is only part of the consideration. Look at it this way: a HOB filter is going to have a higher GPH than a canister for the same exact size tank, yet the canister is a better filtration method, holding a much larger volume of both water and biological filtration (more surfaces for the beneficial bacteria to colonize), most of the time.

So, typically, a narrow area where bio media is stored, such as bioballs, that has a gap at the bottom to allow water to flow through, as well as potentially a sponge or other mechanical filtration pad if filter socks aren't used. The "second" will be accessed (by water) via the gap at the bottom of the first, and will have a gap at the top leading to the main chamber. The main chamber will be a good place to hide a lot of the equipment you need, but don't want in your display, such as heaters, with a mirror image of the divisions from the front leading to the return pump.

OrionGirl said:

poppycock. The balls will be exposed to the water and the air, and moving around. This means there's ample access to everything the bacteria need to survive. The water will move through the system at the same speed--what having them float will do is reduce the number that can be in contact with the water at any given time. Easily remedied by bagging them up, and adding some ceramic cylinders to keep the bag from floating.

One reason to divide a sump is top prevent bubbles from getting into the pump. Without that the incoming water create bubbles, and they go in to the return and create microbubbles in your tank.

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Are you not contradicting yourself? First you say they can free float and have a good effect. Then you recommend to add additional media and bag them so they sink. Which one is it? I have a 90g tank with a 29g sump up and running right now. You will get much better results with the sump divided so you can control the water flow to make sure it goes through the desired media. It has nothing to do with bubbles getting into the pump. I can stop that by just having a filter sock and a return pump. I won't have any bubbles.


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No, I'm not contradicting myself. Free floating will work. Adding enough and sinking them will work better. You're saying the floating media is useless, I'm simply saying that's not the case.

As long as the media is colonized with the proper bacteria and exposed to the flowing water of the system, nitrification will take place. However media which is maintained above the level of the water in the sump and has system water trickle through it is several times more efficient at nitrification than the exact same amount of media which is submerged, due to increased O2 availability. Nitrification is nothing more than oxidation, and air holds A LOT more O2 than water.