The baffles do not have to be a perfect fit if you use glass either. I find it usually easier to cut the piece of glass just slightly smaller than your inside width of the tank and the silicone will fill it in. And as Tony stated it can be a challenge to attach acrylic to glass.

Don't quote me on this... But somewhere in the millions of DIY threads I read that you shouldn't use plexi or acrylic baffles in a glass aquarium (or at least not cut the baffles so that they are too snug).

Basically, long story short... plexi/acrylic expands more than glass and at a lower temperature. If the baffles are tight to start with, the extra expansion could create pressure and end up causing the glass to break.

Whereas, glass baffles in a glass tank (or acrylic in an acrylic tank) would expand at the same rate as the tank structure.

I don't know if it is true or not... Just letting you know that I read it on the internet.

Don't use GE Silicone II. From what I understand it has anti-mildew agents in it that will wipe out your tank.

I was at Home Depot today and both GE I & II have the anti mildew agents. The salesperson said he had nothing that he would trust for aquariums.

They should carry the GE Silicone I for Windows and Doors. It will say 100% silicone on the tube. If it says that your good to go. Do not get the kitchen and bath silicone as that has the anti-mildew agent added.

Ive been using the "GE Silicone I Windows and Door" myself for years and never a problem.

Canadian Tire carries silicone that is good for aquariums. It's in a green and white tube but I can't remember the brand name or anything.

I am pretty sure that I have a tube around here somewhere but I am in the middle of a reno and I can't find a thing.

If you still can't find anything by the weekend, let me know and I'll pop in to CDN Tire and get the product name and details.

BOTH Canadian Tire and Home Hardware sell a brand of silicone that says right on the packaging "Ideal for Aquariums"... no special extra price or anything, only comes in clear or white that I could find, just regular Interior Silicone... get that kind... :mrgreen:

If you really need black... GE 1200 Series construction silicone... but I'm not sure where to buy it.

This morning while I was looking for my car keys, I find the silicone.
Yup, figures I find it when I' no longer looking for it.

Mastercraft Interior & Exterior Silicone 67-0859-0

Description on the back "Ideal for aquarium repair (allow 2-5 days before filling aquarium)"

HTH