Advice on floor support for large tank

[sknoch78]

I am almost to the point of setting up my new tank. Total volume will be around 300g. I have done a tremendous amount of research and have read several threads about supporting the floor but few talk about putting a tank on the mainfloor with a basement. I am looking for anyone who has done this. Here is my situation, Main floor is supported by 2x10's with 3/4 ply and 3/4 oak floor. From the exterior wall where the tank will sit, the joist span aprox 12' before resting on the main cross support for the house. I have limited access in the basement as it is a completely finished daylight basement. I can open up the ceiling for any work to be done. What I cannot do is add support posts of any kind. So here is my dilema, how do I beef up the floor. I was thinking of adding additional josts and cross blocking as well as looking at beefing up the connection at the rim joist with hangers possibly.

Anyone have any good input?

FYI the tank will be 72x30x24 and the space it will occupy currently has 5 joists I believe.

Thanks in advance
Shawn

[wonk]

I'd think a formal consult from a structural engineer would be money well spent in this situation. When you can put posts down or if your weight is by a load bearing wall, I'd say it's much easier to just go with some beefy posts, but with the requirement of no vertical components you are going to have to be really careful. I'd curious myself if just adding more joists would be enough. It seems to me that tripling the joists involved between two load bearing walls would be sufficient. That would be a lot of wood and a lot of work ripping out the cealing, and accounting for whatever is routed through that section (electrical/plumb/hvac).

Any way that you slice it, it's going to be difficult, I'd think.

[jnfallon]

Shawn, I wouldnt doit without adding a beam and posts under the joist directly under the tank.

I just installed a 375g, similiar span, 2 x10's, outside wall, perpendicular. Flooring is pine plank.

I build a fully headered support wall under where the tank sits (I have a finished basement as well) and the tank STILL sank 1/4 inch along the side walls. I assume that indicates the joists are bowed approx. 1/4" even with all that support. I am surprised, as I blocked too, but its a lot of weight.

I almost skipped the post/beams and I am SOOO thankful I didnt.

[grupper]

You might find this information usefull.

http://badmanstropicalfish.com/articles/article28.html

[sknoch78]

Thanks everyone.
grupper, that was a great article. I will be getting a structural engineer out to help me decide what needs to be done.