Question from John in Rochester, NY

Last updated 6/4/17 12:17am


John in Rochester, NY
Submitted 4/28/17

I’ve been following your blog for a while now and have set up an Opae Ula tank using your ideas.

My tank is a “tall” 16 gallon (same footprint as a 10 gallon tank) and I have an under-gravel filter, under about 2 inches of black pea gravel, with two small power-heads up toward the top of the tank. I filled the tank to the top of the glass. I don’t like the looks of a partially filled tank. I bought a “tall” tank thinking that if the output from the power-heads and sponge filter are far-enough away from the gravel below, the Opae Ula won’t experience much turbulence below. I bought those very-low-flow power-heads set on the lowest flow setting. The output from the power-heads is 12 inches from the gravel. I’m also using an air-powered double-sponge filter that I have set to release the bubbles just below the top surface of the water. There doesn’t seem to be much turbulence at the lower level of the tank. I’ve had my Opae Ula just two days, but they are all hiding. Do you think I have too much turbulence, even though the power-head output is set to the lowest, and the bubbles from the sponge filter and the power-head outputs are all happening a full 12 inches from the gravel surface? Hmm… I’d actually like to SEE these Opae Ula… Maybe I just have to be patient…

My tank parameters seem OK, ZERO ammonia and nitrite and 20 nitrate… I cycled my tank for almost 4 months before ordering them. There is green algae on the glass, on the pile of coral rock I have and on the large lava rock I have in the tank. I have an LED light that I have on 14 hrs per day. I’m not using a heater.

I’m hoping the power-heads work out… Or maybe I could create a “pre-filter” in the under-gravel filter riser-tubes using some filter floss? I could attach some tell-tails on the power-head exhaust tubes to monitor output flow… Putting some floss in the riser tubes would beneficially slow things down coming out the power-heads…

I like your idea of a drip mech filter… I may have to ditch the power-heads and connect the under-gravel filter to some kind of mech drip arrangement if my Opae Ula remain too shy to come out…

Keep up your very interesting and valuable research and your enjoyable-to-read blog.

John in Rochester, NY


John, first, thank you for the kind words and my apologies for the delay in responding. A combination of work and question marks with the drip filter system I’m now using has kept me from blogging.

I agree that a partially filled tank looks weird. My 18-gallon is similar to yours (10-gal footprint) but remains only half-filled as an ongoing experiment in avoiding salt creep. Now that the AquaLifter system seems to be controlling creep, I’m keeping the water level at the 10-gallon mark. I’m not sure if added depth will improve the overall environment.

A practical consideration is water quality maintenance. The bigger the tank, the more water I have to deal with, and 18 gallons is a lot to have to mix and maintain, especially since I’m using bottled water. (I’ll be experimenting with tap water dechlorinated by overnight standing. I learned that the water supply in Honolulu is treated with chlorine but not chloramine. A huge difference because the latter is difficult to neutralize.)

Your experimentation with low-power powerheads and sponge filters is also very interesting. Please keep us posted on your observations.

My experiences alone aren’t enough to form valid generalizations. We need as much input from as many opae’ula hobbyists as possible. Thus, your observations are invaluable. Having said this, I’ll share my thoughts.

I’ve been experimenting with the AquaLifter drip filter system for three months now and believe that, in its present configuration, it works best for my tank parameters. All my tanks use this system, from 1-gallon to 10. One of the 10-gallons uses only one pump, like the 1-gallon, and both seem to be fine.

I believe the best filtration system is one with a very slow flow rate. In their natural habitat, anchialine pools, water flow is imperceptible. Water from fresh and sea sources pass through permeable coral and lava rock formations before reaching the pools. The filter systems that I tried in the past were all too turbulent. By contrast, the AquaLifter is rated at 3 gallons per hour. It’s literally a tiny stream of water that barely causes a ripple on the surface. I haven’t found anything comparable anywhere.

The problem, though, is that the AquaLifter + prefilter was not designed for this use. It’s used primarily in sump systems to manage overflow. I had to experiment with different configurations before I got it to work right. It’s fine now, but aesthetically, it still looks jury-rigged. Hopefully someone will come up with a clean and efficient out-of-tank pump-filtration design with a very low flow rate that also looks good.

I check the pumps at least once a day for any signs of leaking. So far, the pump-on-high setup seems to work best. When I had it lower, lifting and pushing water from and back into the tank strained the tubing at the joints and caused leaks. Placed above the tank, half the pressure work is eliminated by gravity and there have been no leaks.

A recurring problem, though, is algae growth in the airline tubing. I know when it’s time to clean them when the flow begins to stutter into drips rather than a continuous flow. So far, it’s been about once a month. Cleaning is simple. I run a long bamboo skewer into the tubes — from both ends for longer tubes — to loosen the algae. Next running tap water through them or, better yet, blowing through one end, will spit out the gunk. This only takes a few minutes. In all cases thus far, the flow was immediately back to normal.

You mention inactivity in your tank. My best guess is that this is a problem. Opae’ula are curious and playful little guys, and they love to explore and swim about. That’s 24/7, even at night when all lights are off. A sign of a healthy tank, I believe, is activity. The more the better. Still, the inactivity you observed was only a few days after releasing them into the tank, so in time they may have become more comfortable and active.

If inactivity is still a problem, you might want to turn off the powerhead and filters to see what happens. If they come out of hiding, then you’ll know turbulence may be the problem. Unlike fish, opae’ula can survive without mechanical filtration for long periods of time (days), so don’t worry about turning it off.

I experimented with sponge filters for a while. However, they had a negative impact on my tanks. In time, they seem to turn the habitat into a wasteland. I’m guessing that they’re filtering out good as well as bad bacteria. But this is my experience, and YMMV. I removed them from all my tanks.

Lighting, too, could affect activity. Opae’ula are known to shy away from bright direct light. You might want to experiment with lesser intensities. Late at night or early in the morning, with all the lights off, check for tank activity with a small, narrow-beam flashlight. If they’re active, then it may be a sign that your daytime lighting is too intense. A solution may be to move the tank to a place where it receives indirect light or brief periods of direct sunlight.

I’m not sure how your gravel and rocks are set up, but the thing to keep in mind is their natural habitat, anchialine pools. They are not like coral reefs or salt- and freshwater fish habitats. It includes both hypogeal (subterranean) and epigeal (surface) regions, and they are active in both. The hypogeal is best seen as a network of subterranean tunnels and caves created by the gaps between coral rocks.

I’ve been relying on Dennis Nakashima’s codominium coral mound for hypogeal simulation, but for my small (1-2 gallon) tanks, it wasn’t that effective. For these, I’m using a strata design, with the hypogeal forming a full layer over the gravel bed. This leaves a wider epigeal layer above for free swimming. This works so well in the smaller tanks (active in both, breeding in the larger of the two) that I’m thinking about doing the same with my 10-gallon tanks. The problem, though, is that creating a hypogeal layer of coral will probably require a lot more coral, adding weight to the tank.

If you have plants — I’m not certain, but I don’t think plants are an important part of their habitat — at least the kinds of plants that we normally see in aquariums.

If you have other inhabitants such as different types of shrimp, snails, etc. — their natural pools are usually limited to opae’ula only and not shared with other creatures.

Re filter material in the riser tubes to slow flow — an ingenious idea! That could work. If you try it, please let us know what happens. It would serve the double purpose of also cleaning the water. One drawback may be that the filter could restrict flow to the point where the powerhead will stop working. Also, the filter could quickly become a source of contamination if it’s not cleaned often.

One of the reasons I moved to an external filter system is that a UGF system ultimately relies on a gravel filter that reaches a point of contamination that could be dangerous if water is not changed periodically. I think this was happening in my 10-gallon tanks, where activity was diminishing over time. When the original filter material in the AquaLifter prefilter gets dirty, I’ve been replacing it with activated carbon pellets. This way I avoid having to continually buy prefilters, which could add up quickly.

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2 Responses to Question from John in Rochester, NY

  1. John in Rochester, NY says:

    Thanks very much for your very nice response. First off, my Opae’Ula are very active now! I have seen berried ones and even little zoeae floating around!

    So,I ditched the power heads. They seemed to generate a lot of vibration, and when I turned them off, the OU came out! I now am using an airstone down in the riser tubes set to a very low air flow. The bubbles break about an inch from the surface and this doesn’t seem to affect the OU activity. It also helps that I have a “tall” tank (19″ tall) so that all the bubbling happens a fair distance from the gravel surface.

    I bought a small canister filter, 10″ high,106 gph, $30 on Amazon, and I may put it on my tank when I think the UG filter space needs some help. For the intake, I’ll stick one hose down each UG filter riser tube, and connect them with a T-fitting and then into the filter. The hose will fit nicely thru the rubber adapter that was on the powerheads, making a good seal with the top of the riser tube, and I’ll stick the hose all the way down the riser tubes to below the gravel level. I’ll throttle the output with a ball-valve fitting, in-line on the output tube, and set it to a trickle. I may use a spray-bar on the output, to spread out the outflow over several holes over the length of the aquarium. They say that controlling the output flow won’t hurt the magnetic drive pump on a filter if done on the “output” side. I’ll pack the canister with filter floss, and monitor the output, and open the ball-valve as the filter gets clogged to maintain the trickle. I’m thinking that a low flow out thru a spray bar won’t create any more disturbance than what the airstones are doing now in the riser tubes, and my OU don’t seem to mind the bubbles at all!

    I don’t have much salt-creep, just one spot on my glass hood. I just flick the salt back into the tank every once-in-a-while. I feed my OU about once-a-week, one tiny pellet of some “veggie sticks w/calcium” I got off of Amazon. It’s really neat to see them swarm around this tiny pellet! I have macro algae(?) growing quite readily in my tank –it looks like a green whispy cloud in my tank. And the OU love to graze on it. It all came from just a tiny amount that was in my bag of OU when I bought them in April. I’ll have to thin it out soon… Or reduce my lighting down from 16hrs…

    I have my tank in a prominent place that I can see often. I’m really enjoying the little buggers!

    And mostly, I love the fact that they require so LITTLE work to maintain!!!

    What fun!


  2. JimS says:

    John: “I bought a small canister filter, 10″ high,106 gph, $30 on Amazon, and I may put it on my tank when I think the UG filter space needs some help. For the intake, I’ll stick one hose down each UG filter riser tube, and connect them with a T-fitting and then into the filter. The hose will fit nicely thru the rubber adapter that was on the powerheads, making a good seal with the top of the riser tube, and I’ll stick the hose all the way down the riser tubes to below the gravel level.”

    Thanks for sharing this detailed information about your experiments, John. This is invaluable information for the rest of us.

    I’ve thought of trying something similar. Because of the high GPH flow of most mechanical filters (canister, in your case), I would probably run it for only 30 minutes every day. This might be enough to sustain the water at a healthy level. This would mean that the tank would be without filtration for all but half an hour a day. I don’t know if this is too little or too much. The frequency and duration would be a moving target until balance is found.

    Too much filtration, I believe, sucks good bacteria out of the tank along with the bad. Too little, and the bad bacteria builds up over time. In both cases, the population gradually becomes less active and declines.

    Unlike fish, I don’t think opae need a constant flow of water or air bubbles to thrive. But they do need healthy water.

    Your plan for filter media sounds good. You might want to experiment with different media.

    Re the riser tubes that serve the UGF — they provide perfect access to the water that’s passed through the gravel. I’m using these tubes with my pumps. The air hose that’s inserted down the tube doesn’t need to go all the way down past the surface of the gravel. It should work as long as the end is below the water line.

    Also, the tube opening doesn’t need to be capped as long as it’s above the water line. I keep the opening about an inch above the line.

    Your feeding experiments, too, are interesting. Be sure to check that they’re also actively grazing the tank surfaces when not being fed. The absence of active grazing throughout the day may be a warning sign.


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