And I'm saying using plywood as a base will have no effect on joist loading. Only on Point pressure on the floor material itself. Acctually, If you had carpet, a plywood base would be a detriment, as it would bow in the middle and not be flat.

Great information everyone, thanks! The house was built in 1991. No 'I' beams, just 2x6s running the length of the house but no longer than 12 or 13 feet to the nearest supporting beam as far as I can see from the furnace room. Hardwood floors on the main floor.

I thought about 24" deep by 20" tall, but not sure if that's suitable as a room divider in my space. The 90 gallon that is there now works perfectly at 18" deep and 24" tall. I have a 4" sand bed which has always worked well for me so the depth of the water is actually only 18"/20". So I figured I'd keep the same height, make it 2 feet longer and give myself a couple more inches to play with.

My 155 is on the second floor and I too was concerned about whether the floor needs reinforcing. From what I understand, 150 gallons is about where one starts getting concerned. I do know you are better off against a load bearing outside wall than as a room divider though. To be totally sure you'd best get an engineer to test the load capacity or just do as I did and fill it up. Any others with big tanks on the second floor??

ya, that was my big concern, the fact that it is a room divider. What it has going for it though is the fact that it is really close to the main support beam, almost like it is up against a wall but not quite as strong I suppose. Also, it runs perpendicular to a bunch of beams, as opposed to if it was up against the wall where it would run parallel to only a couple of beam probably.

You should not have a problem if you run perpendicular to the floor joists and close to main beam that support the joists. I have a 150gal. DT and 50gal. sump under the stand. Dim. of stand is 48" x 30" with a soild base (plywood) which sitting on 4 floor joists 2 x 10. Before I started to fill it I had a plumb bob hanging from the joists in the basement so I can check if the floor was bending due to the weight of the tank. It"s been over a year now with no problems.
Hopes this helps.
Ed.

Are you sure that your floor joists are only 2x6? I would suspect that they are a minimum of 2x8's or 2x10's... If they are in fact 2x6's than I would "NOT" put the tank there without having an engineer coming by to have a look. The cost for an inspection will be much less than having the repair done.

Sorry, I meant to say 2x9s, not 2x6s.

Let's try 2x10's :D

:thumb:

Ya, I thought that was odd too, but for some reason they are measuring 2x9s :-) could be my tape measure or my lack of measuring ability.. but putting one end of the tape measure at one end of the beam, and dragging the tape measure to the length/width/height (whatever dimension you want to consider it), the tape measure reads 9 inches. *shrug*