OK, time for a small update...
We went to the LFS (a different and larger one) and bought a few bits!
We got a Liquid Master Test Kit and ran them as soon as we got home, the results are listed below (and just for comparison we also tested our tap water shown in brackets)...
Ammonia 0.0 (0 in tap water)
Nitrite 0.5 (0.25 in tap water)
Nitrate 50 (0 in tap water)
PH 8.0 (8.0 in tap water)
As the Nitrate is obviously way high we decided to do a water change and as we were doing that we also took out 3/4 of the white stones and added a 3kg bag of smaller black stones (see the pictures below).
As well as changing the gravel and water we also upgraded the air pump to a Sera Air 275R which is a massive improvement and also we decided to add a carbon and wool filter as well (it's made a huge difference to the water clarity).
After the water change we did another test and got the following results...
Re-Tested Nitrite 0.25
Re-Tested Nitrate 25
So with this in mind I'll be doing daily water changes for the next week and testing before and after to make sure that they are working, we are hoping to get the tank in balance again before we have to go away for a week.
On a side note the colours of the fish have already brightened so they were probably trying to blend in with the gravel
The Darker Gravel
The new filter after only 10 minutes
The stones fell off the tunnel during the previous water change so this is only a temporary one for the Loach
The fish don't seem any the worse for the changeover
I'll post more results when I got them but for now I hope you all approve of our changes.