Expanded 6/1/15; updated 7/19/15, 9/1/15, 11/26/15
There are probably as many reasons for setting up an opae’ula tank as there are individuals, but some of the most popular are for (1) display, (2) study, and (3) sale. For all three, a common goal is probably breeding. I have no interest in sales, so my purposes are display and study, and I see breeding as the ultimate sign of a viable tank.
Perhaps the most intriguing factor in this hobby is the possibility of creating a living model of a micro-ecosystem that is not completely but very close to self-sustaining and maintenance free as well as entertaining and fun to observe.
The challenge is daunting but do-able if you’re persistent.
I began this hobby about nine months ago, first out of curiosity about the tiny sealed bottles of brackish water with even tinier red shrimp that’s supposed to survive for years with absolutely no maintenance.
A quick scan of the literature and YouTube videos on the subject quickly taught me that the tiny enclosed systems are unnatural and ultimately inhumane.
Further study showed me that the literature on this hobby is inconclusive and often contradictory. Further complicating matters is that much of the literature is contaminated with commercial interests, i.e., information is manipulated to increase sales. Thus, I decided to experiment on my own with (1) different sized tanks ranging from 2.5 to 10 gallons, (2) mechanical and biological filters, (3) substrate, (4) lighting, (5) feeding, and (6) water change.
Here’s a partial list of some of the things I’ve learned thus far for my purpose of creating a healthy tank that sustains breeding and requires a minimum amount of maintenance. In creating this list, I make no claims whatsoever that this is the best practice, so I’d advise caution in implementing these ideas. I offer this list primarily to generate further discussion on this fascinating hobby.
For a nearly self-sustaining breeding and observation opae’ula tank:
1. Incorporate light and dark sections to mimic the hypogeal (subterranean) and epigeal (surface) strata in anchialine pools. The dark section is critical, and it must simulate the lightless network of tunnels in the hypogeal. It must be extensive, roughly 20% to 25% of the tank volume. Borrowing an idea from Dennis Nakashima, against one end of the tank, farthest from the light source, I use a pile of uneven coral chunks that are large enough to create a wide network of accessible tunnels that reach every corner of the mound. The gaps between the coral must be large enough to allow a gentle flow of waste from the mound to the filtering element, but not so large that they lose the tunnel-like quality that scales with the shrimp’s small size. The opae’ula will spend most of their day in the hypogeal so design this portion very carefully. This is also where breeding takes place and where berried females remain for most of the day.
2. I’ve had the 5-gallon and 2.5-gallon tanks longer than the 10-gallon, but breeding has occurred in the 10-gallon only. I did, however, once see a berried female in my first 5-gallon tank, the Fluval Chi, but I didn’t seen any juveniles, so I’m assuming they didn’t survive or they simply matured unobserved. Conclusion:
10-gallon is probably the minimal size for breeding. Update 7/19/15: 5-gallon is probably the minimal size for breeding.
3. The 10-gallon is equipped with an undergravel filtering system and no other filtering device. The 2.5-gallon and one of the 5-gallon tanks use a sponge filter only. I recently switched the other 5-gallon (Fluval Chi) from sponge filter to undergravel filter. At one point, I used both filtering methods to counter the problem of water that was slightly murky. However, I removed the sponge filter. The water is still slightly murky. However, the water in the 10-gallon is crystal clear. Update 7/19/15: I no longer use sponge filters in any of my shrimp tanks for this reason.
4. Tanks with undergravel filters, obviously, have a substrate of gravel about an inch or more thick. Tanks with sponge filters don’t. The rationale is that a substrate of gravel without an undergravel filter would simply accumulate waste. However, sponge filters may create enough circulation to keep the substrate relatively clean. Update 7/19/15: I no longer use sponge filters in any of my shrimp tanks for this reason.
5. Natural sunlight seems best, and indirect sunlight may be optimum. The 10-gallon is farthest from direct sunlight but receives a lot of indirect sunlight during the day, especially in the late afternoon from the west-facing lanai windows and glass doors. For the 5-gallon on my desk, just inches away from a window with direct sunlight, I’m trying to enhance the dark in the coral mound by blocking about 60% of the sunlight that enters from the window with a piece of black cardboard. I use no artificial lighting for the smaller tanks. All have green algae growth. I use a powerful LED array on the 10-gallon, which I kept on during the day and most of the night, giving the tank only 6-8 hours of complete dark at night. Green algae grew in thick sheets on the glass, draping entire sides. However, they could be peeled off very easily without scraping, with just my fingers. I recently shifted to a pattern of more natural light and less artificial, which means turning the LED on for just a few hours during daylight when the sunlight is weak. This move toward a more natural light cycle, I think, coincided with the beginning of breeding. In other words, opae’ula seem to prefer dark tunnel networks to open lighted areas for most of the day. They seem to emerge from the hypogeal primarily to feed in the epigeal and return to the hypogeal after they’re sated. Update 9/1/15: I seldom use artificial lighting on the 10-gallon. I never use it on any of my other tanks. Re activity: I’m finding that the opae are nocturnal as well as diurnal. You can test this on your own with a flashlight in the dark of night. You’ll see them out and about in large numbers, doing “laps” across the length of the tank. I’m finding that the sign of a healthy tank is a lot of activity throughout the tank both day and night.
6. I tried feeding the tanks with small chips from algae wafers once a week. It attracted the shrimp at first, but after 3 or 4 trials, they ignored it. It seems they lost interest when the green algae started to grow heavily. Thus, I don’t feed them at all and allow natural algae growth to do the job. Update 7/19/15: In the initial phase of a newly set up tank when nutrients haven’t fully formed, I’ve found that feeding a single tiny chip (about a 5th the size of a fingernail clipping from your pinky) from a dime-sized algae wafer may be necessary. If they need the food, they’ll immediately attack it in droves. A single sliver will feed them for at least a couple of days. Feed them more only after they’ve finished the first. Stop feeding when they don’t rush for it. At this point, natural algae is probably established.
7. I did a small (10-15%) water change or two with the 10-gallon and Fluval Chi to counter murkiness in the water. However, I haven’t done it now for months. I top off to control for evaporation using bottled water. Following Christine Ha‘s lead, I use bottled water (whatever’s on sale) instead of distilled water. For brackish water, I add a quarter cup of “Instant Ocean Sea Salt” per gallon of water. (This is exactly half the amount of salt used to simulate ocean water.)
8. I seldom if ever clean the glass on the tanks. When the algae growth became a thick drape across the entire side of two of the tanks, I simply removed it with my fingers. No scraping required. It peeled right off in large strips, leaving the glass clean.
9. I try to keep the tops of the tanks covered as much as possible to control for evaporation.
10. Anchialine pools are close to but not directly connected, at least on the surface, to the ocean. However, they are connected via subterranean channels and rise and fall with the tides. This means that the water in the pools is not stagnant. There’s constant circulation, filtration, and renewal, in both the hypogeal via the ocean and the epigeal via freshwater sources. Thus, mechanical filtration in a tank that mimics this circulation to some extent makes sense.
11. In the early going, I cleaned the sponge filters every few months. I’ve since learned that they’re best left alone and a build-up of matter on the surface is actually healthy. So my plan now is to leave them alone. Update 7/19/15: I no longer use sponge filters in any of my shrimp tanks for this reason.
12. I’m including as much detail as I can to give you enough information to build a tank on your own. The equipment I mention can be purchased at any pet shop. In other words, you don’t need to buy expensive ready-made habitats that purport to be ideal for observing and breeding opae’ula.
That’s it for now. I may add more to this list later.