Conventional wisdom is that opae ‘ula prefer standing or still water. Thus, the belief is that filtration should be kept to a minimum or omitted altogether. The problem is that toxic chemicals such as ammonia build in tanks over time, so some form of filtration may be necessary.
This morning, I decided to experiment with the duration of filtration. I turned the filters off at around 08:00. The plan is to turn them back on in the evening at around 20:00 or 22:00 and keep them running until 08:00 the next morning. The theory is that this partial filtration will be sufficient to control the toxic chemical build-up.
The immediate effect was increased observable activity in all tanks. More opae started to emerge from the coral mounds and swim about.
In the 10-gallon with undergravel filtration, an immediate problem was the open mouth of the two exhaust tubes. The tank was filled to the point where the mouths were slightly under the surface, providing entry into the tubes when the filter is turned off.
I was running the undergravel system without the carbon capsule that fits in the mouth. A quick examination of the capsule, though, showed that the opae could easily pass through the opening and charcoal filler, get into the tube and find their way down into the open area under the gravel. This could be disastrous if they are somehow trapped there or aren’t flushed out when the filter is turned back on.
The glass canopy also limits the height of the exhaust tubes. The cutaway plastic extension in the back that allows access for filters and tubes could be cut back even more, but I want to keep as much of the top closed to reduce evaporation.
The best solution, under the circumstances, was to lower the water level. I bailed out enough to keep the mouth about a half inch above the surface.
This is how the 10-gallon now stands.
The smaller tanks with sponge filters had a similar problem. As soon as the filter was turned off, some opae started to explore the filter opening. A few went in and disappeared into the inner chamber. Some re-emerged, but others are probably still down there. I’m not too alarmed at this point since they’ll probably be flushed out when the filter is turned back on. But I’m a bit concerned that some might be trapped or unable to exit.
Approximately two hours into the off cycle, activity levels in all tanks are significantly higher.
Update 12:00 – Approximately four hours into the test, activity levels were back down to normal. Decided to restart the filters on 3 of the 4 tanks. Left the 2-gallon off since the activity level appeared to remain high.