How do I make my tank safe for new fish?

The neon tetra I asked about in this thread is no longer among the swimming. He was the last surviving fish (both of his tank mates died within the past three months despite looking far healthier than him) so the tank now has no fish in it. I don’t think his tankmates caught whatever it was that made his tail fall off from him, because as I said they didn’t end up looking sick before dying, but I don’t want to take any chances that what he had could have been contagious and be passed along to the next fish I own.

Besides changing the water, what should I do to prepare the tank for new fish? And what’s the best way to ensure that the tank and its contents don’t harbor any germs that would kill the new fish? The tank (5 gallon acrylic) currently contains: half a dozen live plants, a ceramic “house”, a heater, a filter and glass “rocks”. And is there a way to clean the tank adequately without destroying the biofilter?

  1. Neons are not easy fish to keep, so don’t get anymore. They are schooling fish, and they will be stressed out if they are by themselves. Stress = sick when it comes to fish.
  2. Change out all the water, wash the rocks and start over. The biofilter will recover fast enough, though in such a small tank you might want to get an external filter.
  3. Personally I have always had a heck of a time with such small tanks, I currently have a 90 and ~35 gallon tank, they chug along with little effort on my part. The fish in the 35 gallon tank is coming up on being 10 years old, the 90 gallon tank has a happy breeding colony of fish, some of which are almost 7 years old. With such a small tank think about getting a Beta, they do well in small spaces like that.

After many years of keeping fish I think the key to success is to keep the number of fish in the tank low. Just my $.02.

I haven’t kept fish in years but I know a little something about sterility/sanitation in biological systems. I would trash the live plants and either soak the ceramic house and glass rocks in a dilute bleach solution, or put them in a pot of water and let it boil for 10 minutes or so. The heater I would wash well with the dilute bleach solution, and the interior walls and bottom of the tank as well. I don’t think I am familiar with the type of filter you are describing but I would consider just getting a new one if it isn’t too expensive.

I guessed from your other post that this is a new tank. You might want to try something a little less finicky to get your bio filter going. From the description it really does sound like fin rot but then again thewhite spots - were they cottony? That could be a fungus and is nearly always fatal. It is rampant in betas and once they get it, I personally have never been able to cure it. This is what I would do itf it were my tank. Even though it is an empty tank right now, I’d treat it for both fin rot and fungus You aren’t treating fish but the bio filter. Once the treatment is done, do a 1/2 water change that includes scrubbing any rocks or artificial plants, and vacuuming the rocks. If you have live plants throw them out and get new ones. Once that is done, I’d let it sit another week and then check for nitrites. The hardest thing with a new tank is getting throught hte first month with 1st the amonia levels, then nitrites being too high. Once this all stabilizes, try something a little hardier like maybe silver tips or serpae but with a 5 gallon tank, you wont’ be able to crowd too many fish in there.Once you add the fish for the first month REALLY monitor amonia and nitrites and never over feed.

I’m no expert but I have a 30 gallon with tropicals, a 15 gallon with goldfish and a koi pond and once you get the tank going it get s lot easier.

Oh and they ARE a little finicky but for a 5 gallon, one male beta would be really beautiful…just a thought.

K, I play a lot of Battlefield 1942, and was thinking of something different.

Um… um… go over the instruction manual, remove the ammo, and install a govenor?


Keep a second smaller tank running at all times, using the same water as that from your main tank. When you purchase new fish, keep them in the hospital tank for at least two weeks to ensure they are not sick and eating properly. Then transfer them to your main tank.

Completely clean everything in a dilute bleach solution and ditch the plants, as suggested. Rinse extremely well! Make sure you change the filter media as well as the tubing. In the future, make sure you do partial water changes regularly. It is much easier to keep a larger tank, could you perhaps invest in a 15 gallon, keeping the 5 for your hospital tank? It also sounds as if you were crowding your little tank a bit too much.

A great website for you is

Just wanted to add that you should be very careful with the diluted bleach solution, as chlorine will kill fish very quickly. Be very careful to rinse everything well.

Yeah, I forgot about changing the filter but for the chlorine, there are solutions you can buy at pet stores that will help neutralize the bleach.

Without any fish or ammonia input to the tank, the biological filter will die off very quickly.

Your forgot to mention that this doesn’t just happen by itself. For some reason a lot of people seem to think that if they fill their tank with water and then let it sit for a week, the tank will be nice and ready for the fish, when in reality they’ve just wasted a week for no good purpose. I’m not exactly sure what the reasoning behind this is.

Anyhow, the old-fashioned way of doing this was to get a couple of small, hardy fish, let the tank cycle through, then very slowly add more fish. But there is an easier way to do it - go to the store, buy plain ammonia, and add it to the tank every day until the cycle is over (details here).

If your tank was a glass one I’d say go ahead and soak the tank in diluted bleach, rinse, rinse, rinse, soak with a whole bunch of dechlorinator, rinse, rinse, dechlor, rinse, etc., but I’m not sure how bleach would react to the acrylic.

I never saw the original thread until now, but I’m wondering…what kind of filtration do you have on the tank? Did you do regular water changes? Fin rot is very often caused by poor water quality (and, for future reference, CAN be treated).