I have fitted some shelves into an alcove between two chimneys. The shelves
are approx 70 cm across and 30 cm deep. The shelving material is combiboard
(sandwiched plywood) about 18mm thick. These rest on battens 2 cm x 4.5 cm x
(depth/width) which are screwed to the wall on either side and at the back
with nine screws (approx 5cms long) in total (3 x 3).

Would these shelves support a sustained weight of about 60 kg? Reason I'm
asking is I want to put a 10 gallon fishtank on one of them and I don't want
it coming down for the obvious reasons. Any suggestions on reinforcing them
if needed? Or would it be best to just put them on the floor, or bottom
shelf (resting on a couple of bricks to reinforce) to raise it above the
skirting?

Marcus