Filter On, Filter Off: Day 1

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.

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2 Responses to Filter On, Filter Off: Day 1

  1. Christina Nguyen says:

    I was thinking of doing the same thing. I have a set up similar to yours but with a black lava rock hill with a sponge filter in it. I’m a bit worried my shrimp died, I havent seen them since I acclimated and put them in their new home on Tuesday night. Or I thought it might be the filter. I’ll have to shut it off and see how that goes.


    • JimS says:

      Hi Christina. I’m learning that these little guys are tough, so they’re probably alive and well, hiding in your lava rock hill. They’re also really curious. When they sense that the filter has been turned off, they’ll emerge to investigate. Let me know what happens if you decide to turn the filter off.

      Later this afternoon, I turned the last filter back on. Turning it off doesn’t seem to improve activity, except initially. Leaving it on just seems healthier for a small volume of static water.

      I’ve been following Dennis Nakashima‘s lead re a mound of coral rocks and never thought to use lava rocks instead. Christine Ha mentions lava rock in her video and found that opae ‘ula love to congregate on it. She assumes it’s because lava rocks are part of their natural habitat. Following her lead, I’ve added fist-sized lava rocks in my Fluval Chi and 10-gallon. I, too, have found that the opae are attracted to lava rocks.

      Thus, your lava rock hill makes a lot of sense. I read somewhere that the anchialine pools where they live actually extend downward through small openings or cracks into subterranean mazes made up of lava, I assume, or coral — or both. This is where most are spending their time, and the rock mounds that we build in our tanks are meant to simulate this dark maze.

      Anyway, I hope your opae are alive and well — and I also hope you’ll keep me posted on your lava rock hill. I might want to try that, too.


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