Would it help them catch the chromis if they reduce the water level? Don't, know just trying to think of practical plan.
You might not be able to remove every hide but a fish can not hide above the waterline.
I've seen people mention acrylic tank dividers for aggressive fish. Perhaps you could get those and trap the fish in an open corner and then net it from there?
Perhaps you can close off areas and then reduce the water level? (Obviously be careful with that. You can't keep a fish in very shallow non flowing water without any filtration etc for a long time.
There isn't a rush at this stage, can you train the fish to not fear the trap? open the trap put it in the water and feed near it so the fish gets used to it. Then leave it open and feed inside it so the fish gets used to going in, then close it and see if the fish will go in.
Combine all this with hunger and food. If when you feed it comes to the food you could pick an open corner, feed there and be ready to put dividers in to seperate off the corner. Or perhaps even food and then a big net. Like a manual fish trap. Perhaps you have already tried these...not sure just some ideas.
I think the suggestion made there (without saying it) is, if you have to, kill the chromis so you can fallow the tank and then start again rather than risk new fish.
I get that it is a pragmatic solution being offered in good faith, but I am glad you have not jumped straight to that thinking I've lost 29 what's another 1. To that one it's all it has. I would advocate more care for every fish. And as people have said patients is very important in reefing. If you had one diseased fish and 29 happy you might need to take drastic action to remove the one before it infects others... But you don't, so there is no rush at this stage.
Take the challenge. Spend the time come up with a plan and work out how to catch it. You have options.
You might not be able to remove every hide but a fish can not hide above the waterline.
I've seen people mention acrylic tank dividers for aggressive fish. Perhaps you could get those and trap the fish in an open corner and then net it from there?
Perhaps you can close off areas and then reduce the water level? (Obviously be careful with that. You can't keep a fish in very shallow non flowing water without any filtration etc for a long time.
There isn't a rush at this stage, can you train the fish to not fear the trap? open the trap put it in the water and feed near it so the fish gets used to it. Then leave it open and feed inside it so the fish gets used to going in, then close it and see if the fish will go in.
Combine all this with hunger and food. If when you feed it comes to the food you could pick an open corner, feed there and be ready to put dividers in to seperate off the corner. Or perhaps even food and then a big net. Like a manual fish trap. Perhaps you have already tried these...not sure just some ideas.
I can understand the thought that, well this fish is fine so it must not have diseases. That's not necessarily the case. Like people some fish may be asymptomatic, they may get and have a disease or sickness but not have symptoms. They can then transmit to others who can die.May want to reassess risking all future fish vs 1 chromis
I think the suggestion made there (without saying it) is, if you have to, kill the chromis so you can fallow the tank and then start again rather than risk new fish.
I get that it is a pragmatic solution being offered in good faith, but I am glad you have not jumped straight to that thinking I've lost 29 what's another 1. To that one it's all it has. I would advocate more care for every fish. And as people have said patients is very important in reefing. If you had one diseased fish and 29 happy you might need to take drastic action to remove the one before it infects others... But you don't, so there is no rush at this stage.
Take the challenge. Spend the time come up with a plan and work out how to catch it. You have options.