Sure it is, but why not get some of those holders with the sucker feet and a sheet of glass or plastic to fill the gap.
I use a pair to split off small sections of tanks when I have batches of fry to small or young to justify their own tanks.
This allows me time to buy/setup new tanks.
Hello Nordic and ty for your reply
I'm going to have shrimps in the tank and I want something that is going to last longer. I've never done any work with silicone and glass.
And isn't the old silicone going to be in the way of the glass or it does not matter if the glass is touching the tank?
It is not a structural addition, (as long as you allow for a few gaps to equalise pressure on the divider due to possible water volume differences).
You could just hold it in place and silicone the gaps, mask off the area you don't want full of goop first, then pull the masking off after about 5 minutes to prevent it tearing away.
A bit of preplanning and masking off and there are no reasons to make a mess. You lay down the bead, then smooth it over with your finger, work determined and try to only go over once, if you start fiddling with bits that don't look perfect, it goes all rough and nasty.
a.) mask (at least 1 inch tape)
b.) place the silicone bead down with a caulking gun
c.) smooth it out with your finger
d.) clean your finger
e.) pull off the masking tape
f.) clean your finger again, and wait at least 24 hours for curing.