what I do, is get hardy plants. I put them in tap water NO conditioner. now, wimpy plants may/will die, so be warned! I've had to with sword, wisteria and java fern... wisteria died. the others lived :) if you quarantine for 2-3 or more weeks, the disease will die off. the thing about ich, velvet, etc, is it needs a host... no host, it eventually dies.
I've just cleaned my 29 with half and half hot water and vinegar. it's now ready for habitants, after its good tiring cleaning... rocks are next to be cleaned, and all fake plants and ornaments are air dried after basically being boiled