You could try a carbon filter. Dechlorinate a bucket of water and then add a box filter with carbon in. Let it run for 24-48 hours (or until the level drops to 0, assuming it does), then use that water for water changes.
Maybe contact your water supply company and ask why they are adding Cyanuric Acid to your water supply.
Possibly contact the Health Department and newspapers too and let them know the water company is poisoning the tap water with it.
I don't see any reason to add it to tap water and since you're in Canada, the water won't be getting hot and there won't be lots of bacteria growing in it. So a normal dose of chlorine would be sufficient without any additives to make it last longer.