Hi, I have a damaged fish tank and need to replace one of the glass panels, Do I really have to use the special silicone for fish tanks or can I just use the normal high modular silicone as builders use, surely once it has cured it will not give off any thing harmful.
You need to use a silicon that's specifically designed for aquarium use. Most "general purpose" silicon will contain mould inhibitors and, speaking from bitter experience, these will kill all of your fish.