Well, first off, I am back from a long time of not posting here. So, on the off chance someone is interested in my aquariums history since then:

1. Remember that swordtail with the tumor or something? Well, my tank had a little plague shortly after that thing died, even though I had already moved him to a hospital tank. Anyhow, I lost a great many guppies, suffering greater casualties with the younger ones.

2. More recently, the tank got very overpopulated, and my pleco got too big, so I sold the majority of my guppies and my pleco.

I got a lot of compliments on my guppies at the pet shop to the effect of impressive health and size. Even got a good price for them compared to the previous sale.

3. I bought a new pleco, which died right after its warranty expired.

4. I got a new pleco and swordtail male for my tank. Just introduced them recently... However, at around the same time, I noticed some signs of Ich and have already started medicating the tank. I think I caught it pretty early on, and only a handfull of the fish have symptoms, most of them having only very minor symptoms at that.

------------------------

Anyhow, that happening has made me look at my hospital tank. After my swortail died in it, I cleaned it out nicely and left it fish free until present day. Truth is, half the water evaporated out of it between then and now as I pretty much just forgot about the thing. No fish in it, so I didn't leave anything running. I also had no diseases that required isolation.

So, now I look into the thing and think it needs to be cleaned again and made ready for use, particularly if this ich infection gives me a lot of trouble.

I notice that most everything inside the tank is covered in splotches of brown. I take this to be more advanced colonies of brown algae perhaps. Admittedly, it is just a wild guess.

My question: What do I really need to do to get the tank usable again?

It is just a 5 gallon one. It hasn't had fish in it, diseased or otherwise since being cleaned. I have also left the filters and light off since it was unoccupied.

Personally, I would soak it in dilute bleach for a day and then fresh water with dechlorinator for a day to kill anything in there including those brown algae colonies. Before putting the bleach in, scrub it down to get out any solids. You can throw the scrubbie in for bleaching too. I like to sterilize my aquarium and animal supplies (the ones that aren't harmed by bleach, mostly water bottles) before storing them so they are ok for any future use.