When to start over?

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Aquarium Advice Apprentice
Feb 2, 2022
Vermont, USA
Hi everyone,

This question isn't referring to a single sick fish per se, but more of a general question related to higher-than-normal rates of fish loss: at what point do I just completely break down the tank and start over?
I have a 20g high tank set up and cycled for ~18 mo now. I had to move the tank to my office for what I thought would be a short duration for a large home renovation, but that has now turned into a year, and it's proven to be a challenging place to maintain it, due to weekends, work trips, and the unavoidable placement in a spot that gets some direct sunlight (despite keeping the blinds closed as much as possible. but have to keep open periodically for all the houseplants I have). It is moderately planted with java moss, various java ferns, Anubias, and some bacopa. At any one time I have ~8-10 neon tetras and 4-6 cory cats (trilineatus), some ramshorn snails, and 2 assassin snails. It has a HOB filter, and I do 25% PWE every 1-2 weeks, depending on my schedule. Parameters are always 0/0/~5-10 whenever I check, temp 76F.

Over the past year since moving my tank, I would say that I am losing fish at an average rate of ~1/month. Often, the fish will have no symptoms and just show up dead. There have been other times when I've had fish suffering from obvious bacterial infections, probably Columnaris, that I've never been able to successfully treat, either in the main display tank or quarantine tank.

I feel like that is just too high a rate of loss and I am strongly considered just taking everything apart, disinfecting everything, and starting over from scratch. probably when I can move the tank back home, hopefully in another 1-2 months. I understand that a lot of the same pathogens can repopulate the tank once I set it up anew, but maybe 18 months now of experience under my belt and a set-up in a more stable environment will be enough to keep the infections at more of a minimum.

Just curious what other folks would do/have done in this sort of situation.

Thanks in advance...
The problem may be your fish more than your tank. Most Neon Tetras are farmed fish out of Asia so you don't really know the age of the fish you are getting, the general internal/genetic health of the fish or what pathogens they may be carrying. Losing 1 fish at a time is generally a sign of the fish being the problem more than the tank. Tank problems usually effect all the fish at one time. Your water quality seems to be fine which again points to the fish being the problem rather than the tank. So to me, there are no obvious signs that the tank should be " nuked" and restarted.
Since you anticipate having to move the tank in the month or so, I would suggest not replacing any fish that die between now and then and once the tank is back at your house and given some time to get settled, make sure you quarantine any new fish you get for at least 4-6 weeks to ensure that they are not brining in any new pathogens into the tank. You also may also want to consider fish other than Neon Tetras. A good substitute are Cardinal Tetras as they look similar to Neons and many of them are wild caught. ( Confirm from your dealer that you are getting wild caught Cardinals and not farmed ones. ) If you continue to have monthly deaths from unknown causes, at that point I would consider restarting the tank after sterilizing everything and start with totally new fish.
Hope this helps (y)
Thanks Andy, good to know. I like your suggested plan. Everyone had always said that neons were so hardy, so I took that as even further evidence that something must be wrong with the tank if the "hardy" fish were still dropping off.
Thanks Andy, good to know. I like your suggested plan. Everyone had always said that neons were so hardy, so I took that as even further evidence that something must be wrong with the tank if the "hardy" fish were still dropping off.

To be honest, tank bred Neons are hardier than the wild caught ones but you don't usually get larger wild ones so you weren't actually told wrong HOWEVER ( there's always a BUT in there ;) ) farm raised fish come with their own set of issues that don't necessarily effect all the fish. :facepalm: For example, in the wild, when you collect a school of fish, they are generally all of the same age or very close to it. From the farm, you get the fish as sized so you may get a 2 year old runt in a bag of 6 month old smalls or you could get deformed fish in the farmed bag while deformed fish in the wild are usually food for a predator so they usually never get collected. Wild fish have mostly diseases that are the same old stuff as before while farmed fish have developed new strains of the old diseases so you need different meds for them. :facepalm: So you see, each has their issues. :(
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