I am a contractor and i would stronglly advise against it,the issue isnt how much weight the floor joist can bear its how the floor joist is attached. Most floor joists are attached with a saddle bracket which for a period would support the weight,but your problem is a CONSTANT load of over 1400lbs which they cannot support, in time with vibration the nails will pull out. Ok..that said,now you need to determine whether the floor sits on a lower wall or if it sits on brackets....you follow? p.s the wieght rating of an i-beam is over 1000lbs not 600 as mentioned so there is no issue there. Is your basement finished? you could frame up a supporting wall very cheap or buy a steel shoring post anyway I hope that helps. I'm around here alot if you need more info or clarifying. Good Luck sounds like the tank will be worth it

I just saw your drawing and youll have brackets where the 2 joists meet,you need to reinforce that one ibeam that the other ibeams are attached to because that one joist is bearing the weight of all the others conected to it..you follow? bolt a 2x8 into the groove of the ibeam on both sides including between the joists and your probelm is solved about 60$in materials,150ish if you remove drywall. The piece of mind is worth it

Yes, the joists in question are attached by that metal joist hangar (perhaps called a saddle bracket?). Anyway, I fully developed the basement about 5 years ago, and - as it happens- where the aquarium sits is directly above my workshop area and is therefore conveniently open to put whatever support I would need from below. So keepimg in mind it is still my workshop area and so do not wish to take up too much area, would a stragically placed telepost(s) or 4X4 post along that lone joist do it and do I allow for some sinking of the floor or just put the post snug to the joist and concrete floor. Also, the floor, of course, has no poured footing, so is that a concern?

Ok second look at your drawing i see thats a double ibeam what i explained was allready done your good to go put a telepost on the opposite side of the tank if you like to prevent the beam from bowing but i think your good if you dont want to.....no worries Good luck with the tank

Great...thanks very much. I was thinking a telepost where the 2 joists meet plus an additional one 37" down to meet the edge of the aquarium, or is that overkill?

I've got my 145g sitting across 5 joists midway between 2 beams ~10' apart. Though the stand is built in, it basically 2x4" construction.

No cracks in the grout or stone in front of it and I've really got to bounce my 200+ close to the tank to get a ripple.

and a additional comment, during house construction often see about 4 foot stack of drywall or sheeting sitting in the middle of the house. It's got to weight a few pounds and can't say I've seen any lifts ending up in the basement from the floor collapsing.

Floors collapsing under large loads are not very common. It is the sagging of the joists under the prolonged weight that is usually the problem.

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does the stand have a flat base or just edge base hollow in center
because the weight is min if its a flat base not hollow . i have a 180 with a 90 gal fuge and no problems over 5 joists and its about 200 pounds per sqaure foot so i figure i am over 200lbs and the floor hold s me

Let me try to clarify this for everyone,the joists can bear the weight but it depends on how they are anchored,a saddle bracket alone cannot bear the prolonged constant weight. If you people want to risk it its your perogative,but reinforcing costs maybe 200$ what did your tank setup cost? or how much damage you think 100+gallons of water would cause?