I have a cycled, 40 litre heavily planted (java moss, java fern, moss ball & anunbias) nano tank with an eheim powerball sponge filter, heater and thermometer. In the tank are 3 guppies, 1 zebra otto and 6 cardinal tetras, nuisance snails and until about 2 weeks ago, a thriving cherry shrimp colony.
I originally had a 30l biorb that I had retrofitted with a sponge filter which had 50/60 CS and then got the 40l tank and transferred most of the shrimp to the new tank once it had cycled and had run for a few weeks with the new guppies and tetras.
I recently got rid of the biorb (as it is a fishdeathtrap in my opinion) and is now to be a mini balcony greenhouse! So I took the remaining shrimp, anubia (already had plenty of other plants in new tank) and inert black gravel and added it to the existing black inert gravel in the new tank, doubling the depth. So far so good.
Soon after the first water change after adding the old established gravel (about 1" at front to 2" at back now), which would be about 5 months after set up and cycle, I had a couple of shrimp deaths. Unfortunate but didn't think too much of it as thought they had just got in the way of the gravel movements.
1 week later I do my weekly water change and almost immediately afterwards I have a dozen or so shrimp laying on their backs, dead, all over the tank, gravel, plants, rocks. The fish won't touch them.
I thought this is weird so I left it for a bit and everything settled down, but the shrimp seemed less active or visible. Finally after a week with no more deaths did another water change (the usual 25% or 10 litres) and this time it is shrimpocalypse - must have fished out at least 20 in 2 days.
I think I now have about 10 juveniles left, most of the adults have snuffed it.
General tank info:
As far as I know the water is quite soft here.
I normally do a 10 litres weekly, sometimes fortnightly, water change, leaving the water for about an hour with a quarter cap of seachem prime
I have never medicated the tank with any chemicals, apart from the odd few drops of leafzone
The filter is about 2 years old as have never changed original filter, just squeeze it out in aquarium water until water is fairly clear coming out of it.
Fish are fed flake food or frozen bloodworm daily and shrimp get shrimp food every other day. Food seems to be all gone within the hour.
Temperature is a steady 26C
There is a fair bit of green algae and there was brown algae for a few weeks but this disappeared about same time shrimp started dying
Every water change I deep clean about a quarter of the gravel and suck up a few snails.
-guppys and tetras never go after the shrimp themselves, not even the dead ones, but sometimes nick their food - 'tis the aquarium jungle after all
Ok so here is what I have narrowed it down to:
-there was some light brownish chunks of fuzzy gunk that suddenly appeared in the water that the shrimp were chomping on, possibly an accumulation inside the filter? no idea what this was but quickly removed any bits I could see.
-pH in the water is 7.4 but nearly 8 out of the tap - maybe I didn't leave it long enough before putting in as seems to lower the longer it is out the tap/treated with prime?
-apparently the water from the cold tap contains .002ppm copper...is this enough to kill shrimp...? there are still snails, the nuisance kind, in the tank. I am using cold water and letting it get to room temp and then pouring in, but have in the past sometimes whacked on the warm water to make sure it gets to the right temp quick enough. There are also 2 seachem flourish undergravel tabs I put in a few months ago.
-using APi master test kit I get regularly 0 ammonia, 0 nitrite and between 15-20 nitrate (there were still shrimp I did not realise were still living in the then unfiltered, unheated biorb that had readings of .25/5 ammonia and 30 nitrate that I transferred to the new tank when my flatmate noticed there were still some shrimp in the old tank I had missed! so these are hardy little fellas). The nitrate is slightly higher than the usual 10 for some reason-seems between 10-20.
Did another water change earlier after leaving the water with the prime for 10 hours and not having any more noticeable deaths, although the remaining handful aren't looking very active but alive nonetheless....
I have attached a read out of the water from the average of samples taken from the general area too.
Grateful for any thoughts what the culprit(s) might be please. And sorry for the ridiculously long post!