Sorry for the delay in posting, just haven't had the time lately. Couple of things to report
Firstly there is no such thing as a fish that's too fast for the lobster to catch. I added 6 neon tetras which I assumed would be far too quick for him to catch. I now have 5 tetras so I'm guessing one became lobster lunch. He has also eaten a Danio, I knew it was the lobster when half a fish started floating around the tank. I netted it and offered it to him with tweezers, he snatched the remains right back and scurried to his cave to finish it off.
I moved my filter into the corner of the tank right next to his hide and the fish congregated there and they were an easy catch for him. So I think I caused their demise. Since moving the filter back to where it was in the centre of the side of the tank there have been no more losses. Although he is now actively hunting fish. Except for the mollies who seem to tease him relentlessly then swim away when he gets annoyed.
Secondly he appears to be an enthusiastic gardener. I put quite a bit of Java moss and Java Fern in the tank which initially he ignored however the Java moss was soon collected and placed in his den and then slowly eaten. and the Java fern was well and truly pruned. Causing me to have to do a massive cleanup of the tank as the filter became clogged with the debris. I wasn't sure whether to just move the Java fern to another part of the tank, away from his hide so I placed it on a ledge leaving the roots of the plants dangling in the water overnight. He promptly climbed up the filter, dragged them all back into the tank and started clipping them again. Another cleaning up job for me. I think I will just stick to plastic plants for now lol. Although he created the mess he is currently roaming around the tank finding bits of leaves that I have missed and eating them.
Before getting the lobster I had a bit of a snail explosion, one or two must have sneaked in with a plant and soon I could see dozens of them around the tank. This seems to have been sorted out, whether the lobster ate them I'm not sure but it is a possibility as I found lots of empty shells around. After the initial aggression with the apple snail. He seems to have reached a truce with the apple snail, he no longer attacks it and the snail will quite happily sit there while the lobster cleans algae off him which is strange to watch.
Other than the above, it seems he's ready to moult again, he literally looks like he's bursting at the seams. Thanks for the advice about calcium, I have added some crushed coral to the tank and hopefully that will suffice if he does moult soon which seems to be the case it means he is moulting on a monthly basis. He has what look like hairs growing on his pincers which are apparently a harmless parasite. On reading it seems I can wipe these off with a cotton bud but they will just grow back so I will leave them for now.
General behaviour wise, I expected him to be in his cave all day and only venture out at night but he seems to be active all the time, constantly moving about the tank cleaning or "standing guard" outside his cave. When I feed the fish flake food he rushes out and stands in front of the filter grabbing any flakes that come within reach. He claims any sinking food, shrimp pellets and bloodworm pellets and they are stashed inside his cave and then eaten at his leisure
Pictures in following post