29g well established tank died after a routine vacuum - Original post titled "I vacuumed my tank. Now everyone is dying. Update and questions on how to move forward below."

[Paula Blanca]

So as of this this morning the last of the 4 fish in the heavily planted 29 gallon tank was dead. Interestingly I also had one plant completely covered in furry white fuzz. I also noticed all of my bladder snails (hitchhikers, never wanted them) are also dead. The water is cloudy.  (FYI, some snails were still alive last night)

The only thing that changed between everyone being fine and everyone being dead was a light surface vacuum of my sandy substrate and the poking in of a few plants that had some loose roots (less than half an inch, not a lot of stirring or digging in the substrate.)  I did a 30 percent water change and declorinated with stress coat. The tank was up over a year with no deaths. My ammonia, nitrites and nitrates were all within normal limits after the first 2 fish croaked but I haven't retested today.

So now I have a tank devoid of animal life. Seems like a great time to move around some plants. But whatever I did that caused the die off appears to have come from the sandy substrate. What should I do about that? Suck it all out and bleach it? Do a number of super deep substrate vacuums and change the water aggressively? How do I keep the beneficial bacteria going in my sponge filters if I messing around with something potentally toxic in the substrate and no fish are producing ammonia? I have zero interest in breaking down the tank as the plants are (or at least appear at this point) to be healthy and there is quite a bit invested in the lighting and such.

[Fish Folk]

So sorry to hear.

Some questions:

- Can you run a full spectrum water test: pH, KH, GH, Ammonia, Nitrite, Nitrate? 

- Is this your usual maintenance routine?

- What sort of filtration (if any) are you running?

- Have you assessed factors such as temperature? Stray current? Source water contamination? Had pH crashed? Were there any worrying signs that led you to this maintenance?

- Did any large stinky gas bubbles come up as you worked the substrate?

- Can you try to post some before and after photos?

- What was your stocking?

Again, so sorry about your losses. So frustrating. I guess I’d want to figure out causes of death before tearing apart the whole setup. I have heard certain stories about anaerobic bacteria gas releases that can harm fish. This thread from another forum hints at that. I am not sure how much stock I put in that.

[Griznatch]

So sorry about the loss of your tank inhabitants. Any possibility you had something on your hands when doing maintenance and moving plants?

[Beardedbillygoat1975]

I think @Fish Folkand @Griznatchhave this in hand. My sympathies for your loss. Had something similar happen with The Sad Bowl awhile back maybe a year ago or so. I would highly recommend if you do use sand again to put something under it to allow for water flow like lava rock or bags of aquasoil. Hang in there.