Are you sure that you tested it properly and didn't get a false positive? A snail/crab dying is not enough to cause an ammonia spike in that large of a tank that is 2 years old. It would take a very large inhabitant like a fish or a mexican turbo sized snail and even then, a 2 year old tank should at most see a little mini cycle and pose no risk to your other inhabitants.with all do respect, I was asking about the tank, not for comments on my financial situation.
I dont know if i done something wrong, or as I said if a snail/crab or some sort died. possibly my brother might have fed them when he came to visit and its went un noticed. tanks not overstocked as it has 3 fish inside.
I don't think you need to bother with a water change at all.
This is a very expensive hobby, and emergency expenses happen all the time that you need to be prepared for. Bryopsis outbreak, got 2 weeks to shell out $30 on fluconazole or its gonna take over and kill corals. Dino outbreak, there's another $200 for a cheapo UV, pump, nitrate, phosphate, and silicates. Return pump failed, there's another $100. This kind of stuff is part and parcel of the hobby. In hindsight, I wish I had waited until I was much older and more financially independent before I got my first tank. It's been a money pit ever since even though I enjoy it.