I have just done what was going to be about a ~60% water change, but ended up being ~75% as I over fulled the tank.

I disturbed some of the rocks/wood/substrate.

When I turned off the water (hose end in the tank) I had just come from doing the dishes, quickly dried my hands on way to tank and turned off the hose end with maybe still damp hands from the dishwater.

No test kits here so cant test water.

About 350-400 lt of water in a 4ft tank.

Have removed all the smelt and at least 6 have died so far with the other dozen or so not responding well, some in the small bully tank and some in the outside trough.

All the bullies and inanga look fine so far so here's hoping they pull through ok.

Edit:

14 smelt dead so far :tears:

Chlorine in water?

I doubt that residual soap on your hands would be enough to kill the fish but depends on what you use to wash the dishes. Always wash my hands with hand soap and rinse them before putting hands in my tanks.

What were the fish the fish doing before they died? Flashing, Gulping air?

Could have been chlorine in the water, I ask my old man what the water values are for today (works in the dairy factory) as he/they test the water.

The fish started by looking stressed (light coloured) then swimming erratically then fast jerky swimming and then just stopping and floating upside down. All of this would happen within 5-10 min (most in less than 5 min) of the first stress signs.

Even the ones removed before showing any stress died fast once they started to show colour loss.

Some of them you could see the blood vessels in the head/gill covers

Some of them you could see the blood vessels in the head/gill covers

Reddening around the gills is usually a sign of chemical burns of the gills. My guess would be Chlorine.

Does your local supply get treated with chlorine normally?

Wanganui water supply gets regularly dosed with chlorine but especially after large rainfall the council ups the chlorine levels. Our water supply is bore water.

Our water is normally dosed with chlorine, and we have had alot of rain so the powers that be might have upped the dose, but I couldn't smell any extra in the water.

I guess if it was enough to kill fish then my tank will be restarting it's cycle, well at least there is only 1/2 the bio-load in there now :facepalm:

smelt are pretty sensitive to water changes

whereas kokopu etc seem a little tougher

I know that smelt are 'sensitive' but this is the first time that I have lost any from a water change, infact I think these are the first ones that have died other than in the first 24h of being caught.

My tank looks empty

All up I have lost 17 fish, that is all my smelt, from doing a too large a water change (by the looks).

That just leaves about 8 bullies; Cran's, common and maybe a giant bully, 2 koura and maybe 12 inanga in over 350 lt of crisp cold water.

I guess I'll be going on a fish hunt this week/weekend, maybe I replace the smelt with some kokopu?

Very sorry for your losses

Was it only smelt or other species too?

Had the tank been well-maintained before this? Perhaps you stirred up too much gunk from the bottom? I have often done 50-75% waterchanges on natives and had no problem (Palmy water is also chlorinated) but killed everything with a major waterchange and gravelvac after having let maintenance slip for a while.

You may be tempted to use dechlorinators in the future, but these would be toxic to your crays. Can't win. :facepalm:

(I just did a 50% change on my tank with some new smelt, will be keeping a close eye now!)

Was it only smelt or other species too?

Only the smelt, one of the biggest inanga did look a little stressed bu was fine by today

Had the tank been well-maintained before this? Perhaps you stirred up too much gunk from the bottom?

There had been the auto water changer running up until 2 weeks when I disconnected as it needed the window open for the hoses, during the clean I scrubbed 2 of the sides of algae and moved 2 bits of large drift wood and a large stone to make room for another bit of wood (maybe the new wood?), no real substrate movement...

I did a bigger w/c as I wasn't watching the tank, normally only run it 3/4 full it is now to within 15mm of the top

damnit, my smelt were dead this morning too! They looked fine last night. WEIRD.

Amazing how the cucumber smell is so much stronger when they are dead. The cat refused to eat them.

i think it maybe the size of the water change as i had the same thing happen to me after a large water change and they were the only ones effected lost about 5..

I better go check on mine. :-?

Late update:

I talked to my father about the water quality that weekend and the chlorine in the town supply was about 4 times what it normally tests at, that would be the cause then.