30gal Opae tank?

[Fishkeeper]

Hello all,
I have a Biocube 29 standing empty. I don't know the exact size of it, but it's somewhere in the 25-30 gallon range. It's a cube, about 18", and I want to fill it with shrimp.
As of right now, I have a cycled 3.5gal shrimp tank. I've had it up since January 2018, and I haven't had any breed. I think it's too cold- I keep my room in mid-low 60s. They're lively and colorful, and I had a berried one in April so I know I have at least one female, but they aren't breeding. You can't heat a tank that size safely, I know, but I DO have this much bigger tank.

Supplies I have:
About 3 cycled coral rock chunks covered in algae
A couple pounds of cycled sand, again, algae
A decent-sized bundle of macroalgae
10? shrimp
Some non-cycled Hawaiian coral rock (found on a beach, probably contains dead things)
Granite chunks
Reef salt

My plan so far is this;
1: add dead rock and about an inch of substrate to tank, fill with appropriately brackish water
2: add appropriate heater to keep water at about 76-78F
3: cycle tank until dead rock stops giving off notable amounts of ammonia or nitrites
4: add all materials from old tank
5: enjoy

There are no easily noticeable issues in there, right?

Will 10 (or I might get more) shrimp breed in a tank that large? They'd find each other when they wanted to breed, right?

I have a couple of nerite snails, currently in freshwater. Once the tank is cycled, I'm planning to acclimate them over. Anyone ever tried nerites with opae ula? I'm assuming there won't be any issues. Nor should the snails eat all the algae or anything- they've been living in less than 5 gallons of water and eating algae in there just fine, so they shouldn't put much of a dent in 30gal worth of algae-growing space.

Also, I have a lot of empty space to fill up. Any suggestions on where I can get things to fill that space? Safe and appropriate-looking rock, mostly, or some sort of synthetic material. I don't want to mess with lava rock and its potential contamination. Any good sources for dry reef rock?

[Vorteil]

Great plan. I would scrub your rocks as thoroughly as possiblt to remove any dead debris. You have a great size tank to use. I've never had any issues with lava rocks & all 6 of my tank + 2 jars are filled with it.

Maybe this will give you some ideas since I have a tank like yours. One of my tanks I have is a 6 gallon Nano Cube. It should be similar to yours. It's one of those all in one designs. I completely gutter the rear of the tank and also opened upa and removed the slots where the water intake would be for the filter. I completely filled this area with lava rock. The open area of the tank has crushed coral as a substrate and what used to be live rock. There's more than 600 opae in this tank. Most stay in the back compartment. others go in and about the live rock. At any given time I may see 50 or so opae out.

10 opae will be too small a number to start with IMO. I doubt you'll see them often. I think it just depends on the areas they can hide. The less areas there are the more you'll see them. Being in the low 60's is probably on the colder side for breeding. I like my tanks to be in the low 70's preferably around 72 degrees. The opae have been breeeding well in this set up.

Here's the intake that I removed all the slots. Constantly going in & out of.

I am constatnly removing the macro algae when it starts to take up too much space.

March

April

July

All my tanks have nerites in it. They do a great job on the algae.

[Fishkeeper]

I'm actually disinclined to scrub the rocks at all. They don't stink, so it's not like there's a dead crab in there or something, and anything small caught in the gaps will rot away while the tank cycles. Besides, my current tank was set up with rock from this same beach (washed up into the sun and dried out, not collected live), and it got some really interesting algae on it. I think some of the algae spores can survive being dried out, and I don't want to wash them off.

Your tank looks great! What number of opae do you find you can support? I read that tanks can hold at least 100 opae per gallon, which would make this an exciting prospect.

How did you cut the back plastic out without damaging the tank?

I know I won't see 10 opae very much, I just want them to be able to start breeding.

Okay, so they like more like goldfish temperatures. I can probably find a heater that can be set for low 70s. I can tell yours have been breeding well, because you have 600 in there!

[Dch48]

I have 16 in a one gallon tank. One did get berries but lost them in a couple of days. I've only had them for 2 months now. There is no heater or filter. There haven't been any losses and I have seen quite a few molts.

I would start out with at least 30 in a tank the size of yours.

Why can't you heat a 3.5 gallon tank? I have 2 of them and have no problems with heaters. One has a preset that keeps it at 78 and the other one has an adjustable that at the lowest setting keeps the water at 74.

[Fishkeeper]

The smaller a volume of water, the riskier it is to put a heater in. There's less temperature inertia, and many heaters are too powerful. A lot of the heaters that are small enough are cheaply made and prone to breakage. It's not that it can't be done, per se, only that it's riskier than I'd prefer to bother with. Plus, this tank is plastic.

[Dch48]

My tanks are plastic too. The one heater is 15 watts and the adjustable one is 20. You just have to not use too powerful of a unit.

[Vorteil]

I always try to avoid anything that could possibly kill off the tank. My tanks temps in the winter get into the low 60's. I prefer not to heat the tanks. It's when the water starts rising above 80 degress that I work to cool them down.

[Dch48]

I agree with that for an Opae tank. You don't need a heater.

[Fishkeeper]

Okay, so it's unlikely that being in the low 60s all the time is stopping them from breeding? I wonder what it is, then. Maybe the light cycle is wrong.

[Afischer]

How often do you feed? Mine did not start to breed until I skipped feeding for 3 months.

[Dch48]

Low 60's may be an issue. Their metabolism slows down and maybe the breeding instinct lessens as well. I would think 68-70 should be a low point for an Opae tank so maybe a heater would be in order. A bigger tank like that warms up a lot slower when the ambient temperature goes up.

[Fishkeeper]

I haven't fed them yet. There's plenty of algae for them to eat, and there's so few of them. I didn't think it was needed.

Does anyone know if opae need to be physically kept from accessing a heater? They won't stand on it and get burnt, will they? I'd hope they'd have the sense to keep away, and I don't know what I'd do to keep them off. Heater guards are made to keep fish off, they have gaps (which are necessary for water flow) that opae could slide through. But they can't be that dumb, that they'd stand on a heater and overheat without ever thinking to move away. Decent heaters don't get "burn you on contact" hot, you have to maintain contact for a bit to get an issue.

[Vorteil]

You're fine with a heater in there. The opae will even graze off of it. No worries at all.

[Ula Hula]

Mustafa said he had breeding in tanks that he kept outside in San Diego where the low temperature was 39 degrees! These are some hardy shrimp indeed.

[Vorteil]

I had an outside tank that had it's heater accidently unplugged for a few days. All the opae were on their side on the bottom. Not moving. I could tell btthey were still alive so I plugged the heater back in and within 5-6 hours they were swimming once again. No deaths. I doubt that the opae would breed in Southern Ca in the winter, still too cold.