Could you post a picture of the 2 joists and 2 beams in question? I have a feeling you might be good with just sistering the 2 joists and adding some blocking.
What's everyone using for posting photos now, I used to use Photobucket but last time I tried posting pics it was paid only. Been a while lol
My current plan is to just get 2 telepost on sidewalk blocks under the joist that the front of the fish tank is on. Joist are 2x10 and roughly 14 ft long