should my stand 'flex' a little?

have just started filling my tank and noticed one of the cabinet doors now scrapes at the top when i open it.
its a 90 gal tank and a custom stand. the door was very close before so i dont think its moved much, probably less than 1mm
the only part of the stand that isnt bulletproof is the vertical stiffener along the front edge. its about 3-3/4" x 3/4" pine.
have spoken to someone else that has a 4x2x2 (slightly bigger) tank on a shop bought stand using the same member that i'm worried about.
i am assuming that as his stand has been bought, someone must have done some sort of design and determined that member is sufficient to hold the load, and if they were any good at their job they would have allowed a factor of safety as well meaning its more than capable.
he doesnt seem to have any issues, and my stand has a second layer of 'top' on it, and much bigger legs that are slightly closer together, with the top bearing on them directly.

is some small amount of 'flex' in a stand expected or acceptable when the tank is filled?
or should the stand be solid enough to not move at all?
is my glass going to crack?
thanks for any advice

 

a few pics to help

where its up to

the door on the left was close before, but now 'rubs' on the corner when opening. put them on myself, so probably werent straight to start with

looking down the beam that i'm starting to wish was a little thicker

 

nicw stand BTW

 

I'm no carpenter, but I've been doing a little diy stuff. I think that I would not worry about it if it's a new stand. I think it would be hard to make something out of wood that is not going to settle in at all, but if you think it's going to keep doing this than I would worry about it pulling a joint apart a little. I think your fine really. If you push on the stand a little does it wobble or shake at all?

 

My gfs stand has 2 doors and they rub ALOT im not so comfortable with it but its been holding her 55 gallon tank ok for years at this point.

 

i can lean on it without being scared its about to fall apart on me, its on a tiled ground slab tho so isnt going to move alot. was thinking the same, that with that much weight the wood could be forgiven for a little movement, just not sure about the glass. i have 10mm of foam under the tank which would hopefully make up a little difference, just dont want the glass to all of a sudden give up one day with too much sand/rock etc on top as well and crack through.
i guess i'll cross my fingers and give it a go
thanks guys

if anyone else has reason to think otherwise please chime in

 

well if your stand is already starting to flex or bend as you say with just water and by the looks you still have more water to add.,
after you add sand to a 90 g your looking at about 100 pounds of sand and another 100 pounds of rock, thats an extra 200 lbs on top of just water.

i would do some changes to strengthen it up personally

 

could you bulk it up with a 4x4 tword the sag?

You would have to match the stain to the new board though

 

Tile floors are notoriously uneven. The problem with your stand flexing is your tank might be flexing along with it. If it were my tank I would remove the water and shim as best I could to get the stand as flat and level as possible. I also would add a thin (1/2 inch or so) piece of styrofoam between the tank and stand to keep the tank from flexing. You can get sheets of styrofoam at any home improvement store. ( Home Depot or Lowes) This may or may not be an issue but better to be safe then sorry. As far as reinforcing the stand that is up to you but I can tell you that when you place wood on an edge like that it is incredibly strong and should be fine. Good luck.
EDIT:SORRY DIDN'T REALISE YOU ALREADY HAVE THE FOAM IN PLACE.

 

the rock and sand would displace some water as they go in, but thats still a good point. i still dont think it would give way, but i would be a little more concerned with each rock i put in it...

really i guess if i'm asking the question it means i'm already worried about it and should try do something. having a tank i'll worry about defeats the purpose of having a nice relaxing marine tank.

could it be strengthend while its full of water, or would it need to be drained?

the legs are almost 3x3 so a 4x4 would be a tight squeeze anywhere.
a small leg in the middle would probably help, but to fit between the sump and the doors it would need to be unusefully thin.

would screwing and glueing another beam to the inside face of that one be any good if it cant be screwed to the legs?