Concrete pad for large aquarium

MikeInToronto · 01/31/2019, 08:15 AM

I'm planning on having a glass tank with dimensions 120x48x30" in my basement (750 gallons). I've calculated the total weight to be just under 10,000 lbs. The intention is to build it on a stand of sistered 2x6's, spaced every 2', except on the short ends. I added a really bad picture

Alternatively, I could have beams directly on the floor so the weight would be distributed along the entire perimeter. It really makes no difference to the design.

My house is from the 60's. What I can gather from other areas of the house, the concrete is 2-3" and I'm assuming not reinforced. Do I need to pour a new concrete pad for this tank? I've been getting mixed answers; some of these are from people with something to gain by having me pour one.

I know this gets asked a lot but i just need some opinions.

Thanks for any help.

Prairie Reef · 01/31/2019, 08:53 AM

I’m no structural engineer, but looking for equivalent scenarios, my mind goes to hot tubs. A hot tub for 8 holds about 600 gallons, plus the weight of eight adults. I’d maybe check with hot tub installers to see if they ever suggest that concrete floors get reinforced for their products?

halmus · 01/31/2019, 06:57 PM

I’m also not a structural engineer but intuition tells me that you can get away with more weight if you’re spreading that weight out over a large surface area vs a few points where the loading is happening. (A big flat-based stand vs the type of stand with 1” leveling feet at a few select points.)

With my tank 350. (48 x 48 footprint) I bought a steal stand from the manufacturer. Once in place on my basement concrete pad, I shimmed it up 1/4-1/2” off of the pad. It was on an uneven break in the concrete. I leveled everything perfectly. Then, I built a temporary form around the entire base and back-filled that entire area with self leveling concrete until just past touching the metal frame. So, every possible square inch of metal frame is well supported by the concrete. It will be a nightmare to remove, but I sleep well at night.

I’m not sure if that helps, but hopefully conveys the idea. Sounds like you’re on the right track with a beefy stand and lots of surface area in contact with the concrete slab spreading the load.

MikeInToronto · 02/01/2019, 01:14 PM

Thanks!
I looked into the hot tub idea (a very smart idea. Got a lot more info vs. aquarium). Lots of people had built a concrete pad except ironically, the hot tub manufacturer who says your floor can support it.
I was also thinking about adding self levelling to the floor to even it out. Building the form is a good idea.

One of the builders I chose didn’t seem concerned about adding a pad. He said I could but seemed wishy washy about it, as if adding it is peace of mind vs. necessity. I’ll try another builder this weekend to see.

Ultimately it works out to under 25 psi.

I don’t mind adding a pad but having that in the middle of the room when the tank is gone would be a hard selling feature. Not to mention the integrity of the floor after cutting into it.

halmus · 02/01/2019, 01:19 PM

If you do end up pouring a new pad...

I don’t see why they couldn’t break up the necessary area, dig out a little deeper in the ground and pour a new thicker pad in that specific area flush with the existing floor. That potentially solves the problem of future resale.

steallife904 · 02/04/2019, 01:10 PM

I was thinking the above... cut the concrete and dig it out deeper, then reinforce the area and pour new concrete that levels up with the floor. Could possible rent the equipment and do it yourself as well. If its not a big deal for you to do it I say do it, you will sleep better.
I cant say how thick a garage floor is but at my last house that we built in 2011 we parked 2 cars on it and it had cracks in the floor. Figure 2 cars might be in the ballpark or less than the weight of your tank and they cracked the floor over time.... I think I would reinforce. The tank would distribute the weight better though. Still think I would though. Make sure if you do you give concrete plenty of time to dry and cure.

wtac · 02/07/2019, 12:45 PM

Hopefully there isn't any plumbing runs under the slab in that area.

Just a thought...pour a 2-3" slab on top of the original slab.

To make it removable for home resale, drill a few holes in the orig slab and insert short lengths of rebar, say 3-4" at 12"x12" plots so that the new slab does not shift out of position (highly unlikely but I overthink everything

).

Make your form and line the bottom with a thin poly sheet. You may need to put a "wire mesh" at midpoint of the new slab. Pour the concrete and let cure. You can hammer drill out that slab and fill in the rebar holes when the time comes.

01/31/2019, 08:53 AM	#2
Prairie Reef Registered Member Join Date: Jun 2011 Location: Lincoln, NE Posts: 127 Blog Entries: 1	I’m no structural engineer, but looking for equivalent scenarios, my mind goes to hot tubs. A hot tub for 8 holds about 600 gallons, plus the weight of eight adults. I’d maybe check with hot tub installers to see if they ever suggest that concrete floors get reinforced for their products? __________________ Old…75gal/20sump mixed, AI Sol SBx2!, mp40w, Tunze 9006, ca++ reactor, GFO/Carbon. New… ??

02/01/2019, 01:14 PM	#4
MikeInToronto Registered Member Join Date: Apr 2010 Location: Toronto Posts: 147	Thanks! I looked into the hot tub idea (a very smart idea. Got a lot more info vs. aquarium). Lots of people had built a concrete pad except ironically, the hot tub manufacturer who says your floor can support it. I was also thinking about adding self levelling to the floor to even it out. Building the form is a good idea. One of the builders I chose didn’t seem concerned about adding a pad. He said I could but seemed wishy washy about it, as if adding it is peace of mind vs. necessity. I’ll try another builder this weekend to see. Ultimately it works out to under 25 psi. I don’t mind adding a pad but having that in the middle of the room when the tank is gone would be a hard selling feature. Not to mention the integrity of the floor after cutting into it. __________________ 220 gallon SPS-dominated reef, 75 gallon mixed reef, high electricity bills Current Tank Info: 220 gallon SPS-Dominated Reef

01/31/2019, 06:57 PM	#3
halmus Registered Member Join Date: Mar 2011 Location: Golden, CO Posts: 340	I’m also not a structural engineer but intuition tells me that you can get away with more weight if you’re spreading that weight out over a large surface area vs a few points where the loading is happening. (A big flat-based stand vs the type of stand with 1” leveling feet at a few select points.) With my tank 350. (48 x 48 footprint) I bought a steal stand from the manufacturer. Once in place on my basement concrete pad, I shimmed it up 1/4-1/2” off of the pad. It was on an uneven break in the concrete. I leveled everything perfectly. Then, I built a temporary form around the entire base and back-filled that entire area with self leveling concrete until just past touching the metal frame. So, every possible square inch of metal frame is well supported by the concrete. It will be a nightmare to remove, but I sleep well at night. I’m not sure if that helps, but hopefully conveys the idea. Sounds like you’re on the right track with a beefy stand and lots of surface area in contact with the concrete slab spreading the load.

02/01/2019, 01:19 PM	#5
halmus Registered Member Join Date: Mar 2011 Location: Golden, CO Posts: 340	If you do end up pouring a new pad... I don’t see why they couldn’t break up the necessary area, dig out a little deeper in the ground and pour a new thicker pad in that specific area flush with the existing floor. That potentially solves the problem of future resale.

02/04/2019, 01:10 PM	#6
steallife904 Registered Member Join Date: Apr 2015 Location: Jacksonville, FL Posts: 944	I was thinking the above... cut the concrete and dig it out deeper, then reinforce the area and pour new concrete that levels up with the floor. Could possible rent the equipment and do it yourself as well. If its not a big deal for you to do it I say do it, you will sleep better. I cant say how thick a garage floor is but at my last house that we built in 2011 we parked 2 cars on it and it had cracks in the floor. Figure 2 cars might be in the ballpark or less than the weight of your tank and they cracked the floor over time.... I think I would reinforce. The tank would distribute the weight better though. Still think I would though. Make sure if you do you give concrete plenty of time to dry and cure.

02/07/2019, 12:45 PM	#7
wtac Registered Member Join Date: Sep 2004 Location: Toronto and Calgary, Canada Posts: 377	Hopefully there isn't any plumbing runs under the slab in that area. Just a thought...pour a 2-3" slab on top of the original slab. To make it removable for home resale, drill a few holes in the orig slab and insert short lengths of rebar, say 3-4" at 12"x12" plots so that the new slab does not shift out of position (highly unlikely but I overthink everything ). Make your form and line the bottom with a thin poly sheet. You may need to put a "wire mesh" at midpoint of the new slab. Pour the concrete and let cure. You can hammer drill out that slab and fill in the rebar holes when the time comes.