Well, I think he's gone now though I can't find the remains. The shop gave me a repalcement, some of their stock looked very small and thin so I selected a larger one this time. Thanks for all your advice! I've disconnected the co2 controller as it appeared to be giving inaccurate readings. I'm told that the probes don't last so I've ordered a new one. I've checked all the parameters with API and Nutrafin kits and come up with the following. Ammonia 0 Nitrite 0 Nitrate 10ppm GH 180 ppm KH 60 ppm PH 7.4
I know the ph is on the high side but within recommended limits, with co2 back in this should come down slightly. Any comments on the others ie GH & KH.
gH is on the high side for Loaches, they prefer softer water. pH is on the outer limits, and you really need to get below 7 for good health with these. Your kH is OK, a tad on the low side so you may have issues with keeping pH stable.
Given all that and a 200 litre tank I'd still say you're pushing it too far for these fish. You're on the upper limits for pH and hardness, low kH so more chance of pH swings and a highly stocked tank that's not really big enough.
One thing's for sure, you DO need to increase your water change regime to at least 25% every week.