Well the snails are supposed to be super clean and healthy. They come from a very devoted breeder and are kept in quarantine. I don't think it's that but who knows? It could also be the marimo balls While we're on it.
The stones... well I did clean them very well. They are natural and lava stones. Yeah I use a filter. It's not ideal right now as the mechanical filtration pump is inside the tank. I would love not to use a filter and just let it be. But then the algae will come the water will get messy and so on. I mean I could give it a try and just leave it and see what happens. But then all hell could breaks loose. I mean Odin uses a filter right? And I spoke to Dennis Nakashima from Hawaii he breeds over 500 of them for fun just in a tank with lava stones and an under gravel filter. So he too has a filter. I would like to know what options I have if I can't get rid of the filter to have a silent filter that does not disturb the Opaes. It's too strange. I don't understand how people have good tanks with many Opaes with no filter.
Another thing Dennis said is to just use sunlight. He keeps them outside next to his house and they are fine. Sadly that's not possible in my case. It would make sense. They have only sunlight in nature. Partially shady and so on.
fyi, I don't use a filter in my tanks as long as you have surface area in your gravel/substrate for beneficial bacteria. They are the key to clean/clear water in Opae ula tanks imo. As you know Opae ula don't produce enough waste for a filter. I know of Dennis Nakashima's tanks in youtube and it might make sense for a undergravel filter with the number of Opae he has.
hopefully the water changes does the trick and it was some pollutant that got into the water. if not, if i was in your shoes, i would start fresh or take everything out and slowly move them back making sure it is not the cause. good excuse for another tank. =)
btw, what temps you keep the water? also as you know, less light will equal less algae.
Why wouldn't the Opae Ula share his food? Because he was a little shellfish