Yesterday I noticed ALL of my ~10 crypt plants are melting. The tank has been stable for a good few months now, regular weekly 50% water changes, and no problems at all. The odd one leaf has melted in the past, but never like this.
The only thing different was this weekend I didn't do a water change I just topped up the tank with about 5% dechlor water. I didn't warm it up, with it being such a small amount. Could that have done it?
No other obvious changes that I can think of that would cause it.
Should I be really worried? Do I need to remove the melting plants to prevent the fish (Red cherry shrimp and pigmy rasbora) from being adversley affected?
That's quite a dramatic drop to happen over a week. I wouldn't expect it to do any harm to the fish or shrimp in the short term but you shouldn't let it continue. If the KH drops much lower the PH could suddenly crash and that is bad.
Double check the test results and also check your tap water so you know where you stand. It's possible with the heavy rain recently that your tap water is different to how it has been in which case you might need to add some minerals when you do a water change.
Assuming the tap water has not drastically softened regular water changes should sort the problem out and stop it re-occurring.
As to the last question, no crypts aren't the aquarium canary, just a pain in the backside from time to time
If you've not already binned them try putting them in a container with some water and leaving them near a window or such like. Crypts often come back from the dead (aptly, considering their name!) so you may well be able to keep them if you give them a bit of tlc away from your main tank
Oh hi Suey2, no they got binned, with some force too (chucked to the bottom of the wheely bin!)
I did leave one little crypt in the tank, as it only had a few leaves, they've all melted, but guess what - it's growing back nicely now.
I've still got a java fern and java moss, which has exploded and a load of moss balls bobbing about. It looks a bit bare so I might have a look at the LFS this weekend and see if there is a delecate little plant I can use in my nano tank.