White cloud mountain minnows seem to have contagious anorexia - help!

[openerofjars]

I have five (remaining) golden white cloud mountain windows, living in a tank with my ten year old goldfish. One of the minnows is really skinny and won't eat, and I'm worried it is going to follow three of its friends into the sunset. I've had a look online for reasons why this is happening and all fish-keeping websites mention how hardy and easy to look after these little fish are.

What's happening here? Why are my fish starving in the midst of plenty, one by one? Help?

Minnows, not windows! Bloody predictive text.

What's your water quality like?
Are they new to the tank?

Grrr, why did my reply work?

Anyway, if they are eating and pooping OK but still getting skinny then I would suspect some kind of bacterial infection or possibly fish TB- www.aquarticles.com/articles/management/Keefer_FishTB.html
How big is the tank and what's your cleaning regime like?

My cleaning regime has just turned over a new leaf, having previously been a bit slack. I am very ashamed.

I did a full tank water change and gravel scrub on Tuesday. Was going to do half change every fortnight from now on. Will that be enough or does it need to be weekly?

The tank is 40 x 40 x 60, I think.

I have had them about 6 months, apart from my lovely goldfish who is ten.

Is that centimetres or inches?

It sounds like you might be overcleaning a bit, I wouldn't change all of the water or scrub the gravel as you are risking killing off some of the good bacteria. If you don't know about the nitrogen cycle then you should read this because it's pretty important stuff.

Have you got a water testing kit? The liquid type are best and ebay is the cheapest place to get them.

Water changes really depend on how long it takes for the nitrAte level to build up and your water hardness. Every fortnight doesn't sound enough to me, weekly is normally about right and you vary the amount of water you change. For a routine change you shouldn't really be doing more than about 25-30%.

Yeah, sounds like your previous water quality might have been the problem.

I'd go with a weekly change of 25%.

Thanks so much. I actually bought the fish from my SIL who runs an aquatics business but couldn't bear to tell her what I'd done with the poor fish she sold me. I will do better in future.