Experimental Oblong 1.5-gal Tank

Updated 11/26/15, 12/27/15

Oblong Tank 112615A

Experimental tank from an oblong-shaped glass vase.

Experimental tank from a glass vase that’s oblong, wide at the center but very narrow from the sides, tapering toward the top and bottom. Capacity is approximately 1.5 gallons. It’s been running for a couple of months and entering the diatom stage. This is a departure from my other tanks with a coral mound on one end a large open gravel substrate for grazing. I had originally used a layer of small coral chips in place of the gravel, but I found that the opae are able to burrow through the tiny gaps and access the undergravel subterranean chamber.

Closer view of the strata.

Closer view of the strata.

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8 Responses to Experimental Oblong 1.5-gal Tank

  1. Robin says:

    Is there a specific reason you don’t want them accessing the UGF? If the current isn’t slamming them around enough to keep them out of there, I would think they’d find all kinds of yummy things to eat down there.


    • JimS says:

      Hi Robin. Good question. I originally had a charcoal filter unit on the end of the exhaust tube, and my fear was that they wouldn’t be able to get out of the UGF area once they got down there. I observed some of them trapped in the small coral substrata after descending into the UGF, unable to find their way back to the hypogeal and epigeal. That’s when I decided to replace the coral with the black gravel. I also removed the charcoal filter to reduce the splash that caused salt to crystallize on the outer edges of the tank. This would have provided an escape out of the UGF, so their becoming trapped is no longer an issue. If I turn the UGF off, they’ll probably automatically explore the tube and descend into the UGF.

      Re nutrients, I’m assuming that the nutrients are primarily in the epigeal level where sunlight breeds algae — and not in the UGF where water has been filtered by the gravel layer. But this is an assumption, and I may be wrong.

      My primary reason for this hobby is observation. I want to be able to see the colonies grow. Thus, I’ve set up the coral mounds that simulate the hypogeal layer to maximize visibility. The experimental tank has been especially designed to facilitate observation. It’s thin front to back and wide side to side so I can see more of the action in the hypogeal. For this reason, I don’t want the opae to hide in the dark subterranean recesses of the UGF. Given their nature, they’re drawn to the darkest, deepest, narrowest places.

      A question for me is why they’re drawn into the gravel substrata that acts as a biological filter in UGF systems. It’s probably because, as you’ve said, they contain nutrients. I notice in all my tanks that they spend a lot of time grazing the gravel. However, they also spend a lot of time grazing the green algae that grows in sheets on the tank walls and in clusters on the exposed surface of the coral and lava rock.

      I’m wondering if another explanation is that they’re drawn by the suction of water through the hypogeal and gravel, which simulates the flow of water to and from the sea in nature. If this is the case, then they’re following a natural instinct that allows them to explore networks of underground crevices that might lead to discovery of new anchialine pools or to older pools that are somehow part of their DNA.

      Re the turmoil of currents in the epigeal in UGF systems — it’s not as bad as it seems. They’re not tossed around unless they’re at the point of exhaust, which is a small area in the entire tank. In the tank as a whole, they swim about with no problems. In fact, in the 10-gallon and 5-gallon Fluval Chi, breeding is ongoing. In the 18-gallon, I saw my first berried female.

      I’ve also observed them routinely enter the exhaust current in what appears to be play in which they allow themselves to be swept along for a short distance. Surfing?

      They’re also powerful swimmers. If you’ve ever felt them bump against your hand while cleaning the glass from the inside, you’ll know what I mean. Thus, unless the current is excessive, I think they’re fine.

      Re cycling: My tanks seem to cycle quickly into the diatom then green algae stages so I haven’t felt the need to keep opae out of new tanks until the cycle is complete. To speed up the process, I’ve transferred coral, covered with algae, from settled tanks into new tanks. I’ve also transferred portions of water from established tanks into new tanks.


  2. Robin says:

    Hey, Jim! There are nutrients under your filter plate. While the gravel catches a lot, the finer stuff (think single celled algae and crumbs from where they’re picking) makes it through and can collect as a sludge under the plate. Back in the ‘70’s (no, let’s not discuss how old I am 😀 ) the uplift tubes were not much wider than the width of a pencil and it was thought that the UGF helped turn the waste and debris into ‘soil’ of a sort and was good for the aquarium and plants. Well, it did, sort of. Now they know that the ‘composting/rotting’ debris produces ammonia which, of course, eventually becomes nitrate. So, fertilizer, but with high nitrate levels and increased osmotic pressure. Now the uplift tubes are larger for better circulation and running your siphon tube down under the plate to suck out the sludge is part of UGF maintenance.

    Your comment about the opae hiding down under the UGF makes total sense. I was just thinking along the lines of filtration and debris. (shakes head) But that would be one big ‘ole cave down there for them and with food down there your viewing pleasure would be extremely curtailed.

    I like your hypothesis about the current also being an attractant. There is food and bacteria trapped/growing in the gravel since it is the filter, but with the opae having a subterranean history, it makes sense that the current would trigger an instinct for exploration.

    You know, I liked finding this blog, but now you’ve got me thinking about all kinds of ways I could dink with these shrimp. And this was just supposed to be about me setting up a nice little tank on my kitchen table for relaxation! 🙂

    As for the current issue, that was one of the, ‘Oh, good!’, things about finding this blog. I wanted filtration. I just couldn’t get comfortable with the stagnant environment way of doing opae. But I prefer UGF’s over sponge filters and didn’t know if the opae could handle the current. Clearly they can, or you wouldn’t be having success with your shrimp. I also found this video during my extensive web surfing that I think you will enjoy as well: https://www.youtube.com/watch?v=B8pyo5tfuxY

    Thanks again for taking time to talk to me about your tanks!


  3. JimS says:

    Hey Robin. I’ve kept tropical fishtanks, off an on, since childhood, and I eventually reached the point where I abandoned the idea of substrata and live plants because of maintenance issues. I ran with UGFs topped with powerheads for a while, too, but gave up when the gravel-cleaning task became overwhelming. For the vacuuming, I used the accessory that came with the Magnum HOT filter. For continuous mechanical/biological filtration, I used a standard unit that hangs over the lip of the tank with a biowheel. I used the Magnum from time to time to clean and polish the water.

    One of the things that attracted me to opae’ula is their return on maintenance (ROM?). YouTube videos by Dennis Nakashima were especially intriguing, providing a lot of raw firsthand observations that got my wheels spinning.

    He doesn’t use any sort of mechanical filtration and relies solely on the currents within the tank generated by heat fluctuations caused by the sun. The coral mound also aids in this current cycle by its shape, position, and composition.

    And he never cleans the substratum composed of tiny bits of coral and shell.

    The fact that his tanks have been thriving for years made me think that maybe the cycle of waste in opae’ula habitats differs from that of fishtanks in critical ways, and one is the level of nitrate. I haven’t tested the purely biological natural current idea yet, but my experiences with sponge filters and UGFs seem to confirm this. I also don’t use a water-testing kit to keep maintenance levels low.

    I eventually abandoned sponge filters because they seemed to be curtailing some of the “good” bacteria. They also took up a lot of space in the relatively small tanks.

    Currently, in my typical opae’ula tank, with a coral mound at one end over a gravel substratum and chunks of lava rock in otherwise open areas, gravel siphoning would be difficult if not impossible. Also, the opae are tiny and could easily be sucked into or crushed by the tube.

    I periodically wipe algae from one or two faces of the glass tanks to maximize visibility, and in doing so, I usually brush against the gravel. Debris from the glass and roiled gravel spreads in the water, but it doesn’t appear to grow as dense or diffused as in fishtanks. In fact, the water clears very quickly.

    Also, the opae become excited (not agitated) by the debris and emerge en masse from the hypogeal to feed.

    I’m not sure what to make of this, but my initial take is that gravel cleaning in UGF opae’ula tanks isn’t necessary. If this holds true, then this hobby continues to push the low maintenance envelope.

    Only time will tell. I’ve been experimenting with opae’ula for a little over a year, and with UGFs for a little less than a year. I have yet to clean the gravel, and the tanks seem to be healthy. I’m keeping my fingers crossed.


  4. Robin says:

    Rolling my eyes here. Wish I’d known you’d kept fish tanks for so long. Nothing like preaching to the choir. Sorry about that. (Did I miss this in your posts?) 🙂

    I cannot -not- have plants etc. in my tanks. I love the look and if things are a little crowded I use them to mark out territories. I’m not into anything exotic, I can’t afford the lighting set-ups to go crazy with the plants. And no huge tanks. But I love the plants. Unfortunately, gravel cleaning does get to be a pain and when shtuff goes south around here the tanks get overgrown with too much debris (like now) necessitating more frequent water changes. And sometimes a tank strip. But fish are so soothing to watch and there is always something going on so, well, there ya go. I’m a sucker for punishment.

    Your description of the shrimp coming out to feed when you disturb the gravel made me laugh. Vacuuming the gravel is a two-handed job for me because my fish do the same thing. The worst offenders are the catfish and bettas. They get so excited when they see the tube coming! So, one hand holds the tube while the other hand shoves all the idiots out of the way so they don’t get squished or slurped. 😀

    A year of no gravel cleaning! I like hearing that! I’m going to start pulling things together and setting things up so I can get my shrimp tank going. A small 2 1/2 gallon for my table. I’ve got a pretty good idea now how I want things but I keep smacking my own hands and telling myself, “Keep it simple!!!!”. My daughter rolls her eyes when I say that and says, “Uh huh.” 🙂


    • JimS says:

      Hey Robin.

      Re tropical fish — you’re right. I don’t think I’ve mentioned it here. My fish have been reduced to a single redtail shark, which I moved from the 18-gallon to a 1-gallon water-purifying plastic tank with a spigot and a sponge filter. No gravel. No plants. For reasons that I don’t fully understand, I’m drawn to opae’ula, so the redtail shark will be my last tropical fish.

      Re plants: I hear ya. I’ve had real and plastic ones in my fish tanks over the years and gradually moved to all plastic for easy maintenance. But the plastic eventually succumbs to algae and are difficult to clean. I agree. In fish tanks, plants are a must.

      I actually experimented with a plastic plant in the 5-gal Fluval Chi but removed it after a couple of days because it just didn’t fit “right.” Seemed out of place in an anchialine pool setting. But that’s just me…

      Re your plans for a 2.5 gallon opae’ula tank: Assuming it’s the standard size, if you’re going with a UGF or sponge filter, make provisions for surface splash, which can quickly become a problem in a brackish water tank. Salt will begin to crystallize on the outer edges and grow if not routinely cleaned. This happens even if you have a glass canopy.

      This means creating a buffer between the surface and the top edges of the tank walls. In my 5-gallon, the buffer has worked down to 2 inches from the top. With a UGF and gravel substratum plus the buffer, the epigeal habitat is reduced quite a bit.

      I’m not saying this to discourage you. It’s just something to think about. Best wishes in eventually setting it up.


      • Robin says:

        Thanks! It’s in the works as we speak. I’m going to deal with salt creep in the beginning ’cause it’s such a small tank. If it gets too annoying, of course, I’ll have to re-do things.Only time will tell!


  5. JimS says:

    Keep us posted on your progress. Btw, Christine Ha has done some amazing things with plants in her opae’ula and other tanks. Approaches living, organic art.


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