Sump Foam Form

That strange object is my aquarium sump. What, you ask, is a sump??? A sump is where the water goes when it flows out of the aquarium display tank. “Ah,” you think, “ask a silly question, get a silly answer!” But seriously, the sump is a place to put heaters, a foam fractionating protein skimmer, pumps, additional bio-filter materials like live rock, etc. This keeps some of these items out of the very limited space of the display tank. Think of it as the deep ocean past the edge of the coral reef.

The sump is a bit over seven feet tall. Actually, it was eight feet tall but I had to cut off about a foot to get it to fit through the doorway into the bathroom. A minor oops! In addition to being a place to stow away equipment the sump is also a way to increase the volume of the water in the aquarium. A larger water volume means more stability both thermally and chemically. That’s good for the fish, corals, plants and other little life forms living in the display aquarium. Thus I want it as big as I can get away with – a trick in such a tiny cottage. My original goal was 20,000 gallons. I’ve scaled it back to a bit over 300 gallons – more reasonable in a 252 sq-ft home that also houses five humans and several other 50 gallon fish and planted tanks. This does mean I have had to trim my life from list of the larger marine mammals and sharks. Oh, well…

To make the sump Will used silicone to glue sheets of 2″ thick rigid pink insulation together to make a box. One of the reasons for the foam is it is a great insulator. Since this is a tropical coral reef aquarium it is warmed to about 80°F. Our house is never that warm. If the sump and tank were just concrete they would rapidly lose heat to the cooler house. Everyone admits that would be too warm. By using foam form work and then completely encasing it in a skin of concrete the sump will keep the water warmer and be structurally strong. Interestedly, someone in a southern climate would have the opposite problem with a coral reef tank – they must dump heat and use refrigeration or evaporative cooling since the water must not get over about 84°F for optimal health of the inhabitants. We have the opposite problem as it rarely gets to 80°F here even in the summer.

Over the course of weeks we poured each side of the box in turn by sloshing in a self-leveling mix of fine sand based PVA fiber ECC concrete with the sump on its side. Each side was given several days to cure before we would rotate the box and do the next side. After doing all the sides we did the corners to buttress them and then poured the base.

Sump Looking Like a Coffin

The resulting sump weights almost 300 lbs. Moving that around in a tiny cottage is quite the trick even with three adults! If it was just a solid rock of 300 lbs I would have no trouble with it. But at 8′ x 2′ x 18″ the sump is extremely awkward to move, especially through a small space.

Bathroom Tub / Shower Area Awaiting Sump

That is the problematic pad. To the lower left of the photo above you can see the bathroom bottle wall which is below the bathtub arch. Pouring the sump pad made the bathroom floor too high to get the sump into the room. We managed to get the sump’s base into the bathroom and were tipping it up into place, the top of the sump was still outside the bathroom, when we had our oops moment. The sump was too tall to go through the bathroom arch! How odd. We had tested this prior to putting in the concrete, back when the sump only weighed a few pounds, and it had worked fine, clearing the arch by a hair. After much thought we realized that the few added inches of having poured the base pad for the sump had changed the dimensions of the room enough to make the sump no longer fit. Eek!

Out we came again. After much debate I drew a line in the sump and applied the diamond skill-saw blade to the problem. The resulting slightly shorter sump easily fit through the bathroom doorway. We tipped the sump to the west, applied a fresh layer of mortar and tipped it back. After bracing it in place we mortared the rest of the edges of the sump to the north wall of the bathroom. Phew! The sump was finally in place clearing the way for important projects.

Sump Drain & Interior

There is a 1″ pipe from top to bottom embedded in the thickening of one wall. This will allow me to use the sump as a settling tank to drain off mulm when I do water changes. The pipe also T’s to act as an overflow incase of a system ‘event’ – just in case.

Cut off Sump Top

One neat thing about the oops is I got to examine how well we did with our sloshing self-leveling pour in the sump. The above piece of concrete is what we chopped off. Basically it is a box beam. It is very strong – it holds my weight easily – even now before being fully cured. This gives me ideas for building big bridges…

As you may have noticed, the sump is not a rectangular cross section. The angle is so as to make the bathtub and shower space a little bit bigger. In cubic feet it doesn’t make a lot of difference but in perception the difference is huge. This angle matches up with the angle of the bottle wall creating a long space in the otherwise small bathroom. Part of my trick fitting a six foot bathtub in a five foot wide room.

Cut off Sump Top

Voila! The sump in place. The tall piece of pink foam along the north wall through the bathroom doorway is all you can see of it now. The next step is parging it with a stucco coat making it structurally stronger, protecting the pink foam insulation and blending it into the walls of the room. A magic trick – making a coffin sized pink box disappear in a small room!

In front of the sump at the bottom is the beginnings of the bathtub. To the lower right of the foam form near the marble pillar you can see the return for the pump to hot tub jets.

I won’t get to use the sump for a long time but I had to build it now in order to build the bathtub to build the bathroom so we could move in before Christmas. So it goes. Still to do on the sump before it can be used is to seal it with a special coral safe sealer and epoxy paint. That’s a project for summer when we can be out of the cottage and not breath the fumes. I’ll probably also tent it and vent it.

In the end there will be the coral reef display tank which will be viewable from the bathroom and the master bedroom, the sump and an additional connected refungium aquarium tank up in the attic utility room. Call it the Sea on the Mount if you will. Since I’ll never go to Bali, Fiji, Australia or places like that instead I maintain a little bit of the ocean here in Vermont where I can study it. I’m a closet marine biologist…

Outdoors: 25°F/11°F Overcast
Farm House: 62°F/56°F
Tiny Cottage: 49°F/38°F Parged shower & sump with white concrete

It’s a lot more environmental friendly to have an aquarium than to jet around the world like Al Gore spouting hypocrisy. Aquarium keeping is an important way to teach people, and especially children, about our natural world so they’ll appropriate it and value its preservation. My message for the day.

About Walter Jeffries

Tinker, Tailor...
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6 Responses to Sumped

  1. Lisa says:

    Wowwhee! That’s some project you’ve got there! CAn’t wait to see the finished setup with fish and everything!

  2. Amazing. I hadn’t really grasped what the “aquarium” would be- that’s going to be really cool.

  3. Jason Larabee says:

    Looks great. Have you thought about how muc hthermal mass that huge volume of water is going to add to your cottage? I remember you posting before about how the termal mass of the cottage was important to its energy efficiency. Isnt water a better storage medium than stone?

    Really cool — Keep up the great work and keep on posting. I love reading your progress. It inspires me! Some day I hope to build to and youve given me a lot of great ideas for my house.

  4. Jason,

    Yes, the aquarium adds a lot of heat storage capacity to the house. But, I can’t really use it well for us since I have to maintain it with the needs of the aquarium inhabitants in mind and they need more heat than us. To really be useful for heat the tank would have to be far larger, like in my dream designs.

    While water is a better storage medium than stone or concrete it is much harder to manage and leaks would be a big problem. I have done it before but this time decided to go with solid state storage for most of our heat.

    The advantage of stone and concrete is that I can incorporate it throughout the construction so it provides not just thermal mass but also structural support. The stone is also beautiful, maintenance free and will last for ever from a limited mortal point of view. :)

    There will be a water tank up in the utility room, a wet space, which will be heated by thermo-siphon from the front shelf solar hot water heat collector and thermo-siphon from the wood stove. That will act as a preheater, and probably most of the time only heater, for our domestic hot water. If I find it collects enough heat then I may set it up to also run to radiant heating coils in the floor (active) or ceiling (passive).



  5. karl says:

    Wow, has it been seven years already? Did you ever employ this sump for a coral tank?


    • Not yet, I’ve been busy building out another large tank project which I just completed. Maybe this winter I’ll finally put in my marine aquarium in the bedroom-bathroom wall. I’ve been thinking about it for the last few months. Then after that is in place I’ll setup the sump.

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