The sponge filters have been running for a little over a month, so I decided to clean the one in the Fluval Chi (below), which has been running the longest. I rinsed it out over a faucet in the kitchen sink. I started slowly, with a plastic container
underneath to catch any opae that might’ve been trapped in the filter. There were none. The filter was very dirty and definitely needed rinsing. I followed up by cleaning the filters in the 5- and 2-gallon tanks. There are approximately 20 opae in each of these three tanks, and they apparently generate a lot of waste. In the 5-gallon (above), the large flat surface on the top of the filer was covered with droppings that weren’t being absorbed by the sponge.
The early pioneers of opae ‘ula ecosystems didn’t use mechanical filtration systems, didn’t do water changes, and didn’t clean the glass. This low-maintenance feature was one of the main advantages that attracted hobbyists. Considering the amount of waste caught in the filters, I find it difficult to imagine going without filtration.
However, there’s always the possibility that the “impurities” rinsed out of the filters are actually good bacteria that’s necessary for a healthy tank. In any case, except for the 5-gallom, I haven’t done any water changes so I’m assuming there’s enough good bacteria in the water to offset any that might’ve been lost in the rinsing. I do water replacement, though, to control for evaporation.
For the 5-gallon, I did a 20-25% water change to correct for murkiness. It worked, and I haven’t had to do it again.
As for cleaning, the diatom build-up on the tank surfaces blocks visibility so I’ve had to clean about once every week or two. The assumption is that diatoms are a natural part of most tanks in the initial stages and will gradually disappear and be replaced by growths of green algae. I see this process happening in the 5-gallon, which is in the south-facing window and gets a lot of strong indirect sun.
In the Fluval Chi, diatoms covered the coral pile and the brown color was nasty. However, seemingly overnight, the diatoms “disappeared” and the coral was back to its natural mostly white color. I can also see the beginning of green algae growth on the east end of the pile.
In all three tanks with sponge filters, I’ve had to scrub the glass with a scratch-safe pad to maintain visibility.
Re turning the filter on and off:
10-gallon: I now keep the undergravel filter off during the day and turn it on from late at night to early morning. Activity seems to have increased as a result.
Fluval Chi: The tank design has been a challenge for its location next to a lot of electronic equipment. With the sponge filter turned on, controlling evaporation and salt crystallization around the edges has been difficult. My plan is to turn the filter off during the day and turn it back on at night with a hood of some kind as added protection against the dispersion of salt. Right now, I’m using a sheet of aluminum wrap as a makeshift hood. Ugly, but it’ll be used only at night while the filter is on.
If I had to do it over again, I’d definitely go with an undergravel system for all the tanks. Waste is pulled into the gravel and, I assume, “processed” and then released back into the tank as healthy bacteria. This would remove the filter from the tank, freeing up space and eliminating the need to rinse the filters once a month.
But I’ll have to wait and see how well the undergravel system works in the 10-gallon before making changes in the other tanks.