How can I make sure my goldfish tank is free of Ich?

[froglegs]

Long story short, we are fairly certain that a newcomer to our goldfish tank (should have used a quarantine tank (blush) stupid, I know, I already feel bad, please don't beat me up too much..) brought in Ich. I haven't dealt with Ich in 10+ years and got complacent about it.. bad idea. I've never had any issues with a fish from this particular store, and they have a great reputation, so I'm wondering if the infection was somehow dormant in my tank, but anyway.. I am sorry to say that despite treatment, both the old fish and the new one died. :(

My question is, then, how can I make sure it is GONE before we get any more fish--I don't want to cause any more fish deaths, inadvertently or not. The tank is a 20gallon acrylic and is an absolute bear to reposition, so I'm hoping this can be done without having to move the tank/empty the gravel.

Thank you so much for any suggestions. :goldfish:

[MCHRKiller]

If you leave the tank empty for 2-3 weeks, the Ich parasite will die due to not having a host. Of course unless you start feeding the tank with pure ammonia your bacteria colony will die and youll have to re-cycle the tank anyway. Before adding new fish do a good clean of the tank vacuum the substrate and do a large WC, just like with fishless cycling.