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Hi, all.

I take care of a 150g rainbowfish tank for a local business. I've had a couple black marble hoplos (Megalechis thoracata) in there for a few months, and I like them. Fun to watch, peaceful, not fussy, not shy at all. Trouble is, the plants in this tank are constantly covered with dirt. Not algae, just dirt. Since this is a dirt-under-sand planted tank, this would seem to indicate that something is digging when I'm not looking. Hoplos are my prime suspects: I keep reading that their time of greatest activity is at night, and that they like to dig. There are two of them; they are growing rapidly, and the problem seems to have gradually come on about the time I put them in as youngsters.

Anybody have a lot of experience with this species? Anybody else find them rearranging the substrate too much for the plants' good health?

Just for background, here's what else is in the tank at the moment:
6 Feeder guppies (or Poor Man's Endlers, as I think of them)
c. 24 Assorted Largish Rainbowfish: Bosemanis, Red Irians, Australians, Red Lasers, Yellows...Maybe one or two other kinds.
10 Emerald Cories/brochis. (Also a suspect, but they seem to limit their digging to the top layer of sand)
2 Spotted Hoplo catfish
A few Amano shrimp (not sure if any are still alive)
1 Bamboo shrimp
Quite a few Mystery snails.

If it's them, they're going to have to go, but I don't want to rehome them unless they are really the problem, and I've never caught them in the act. I would appreciate any thoughts/experiences. Thanks!
Thomas

I never caught them digging

I used to have a trio of these, they used to stick their nose into the sand, about as deep as a cory would, but then spit or puff out water to disturb the substrate when looking for food.

I wouldn't say they dig, but if the top layer of sand above the dirt is only thin I'd imagine they could disturb the dirt. As they are so much fun to watch, could you consider topping up the layer of sand slightly to see if that helps?

Thanks. I suppose I could put in more sand. The sand layer is about 2" thick in most places already, though it's a planted and aquascaped tank, so there could be some thin spots. Adding substrate to a tank like that poses its own problems...I'll have to give it some thought.

So, you two find that hoplos aren't major earth movers. Looking over that stocking list, any other ideas who the culprits might be? I'm stumped.

T

I would say that Hoplos wouldn't move 2 inches of sand out of the way when they are just searching for food. I don't think I would want to add more substrate either, I hadn't realised it was that thick.

I'm no snail expert, but could the mystery snails be burying themselves and bring up dirt with them when they re-surface? I wouldn't expect anything else on that list to dig up substrate. I guess the other consideration may be that someone working at the business is trying to be helpful and attempting to clean the tank or move plants?

Could you somehow quantify the rate of dirt sediment formation on the plants? How long does it take to go from clean to objectionable? Or maybe pictures before and after a known time period could help.

I am a bit surprised the dirt even stays on the plants because my hoplos used to work every surface in the tank. Same for my cories. But my experience with both was relatively short - a few years - and it was that of a newbie. Also, my substrate was either fine or large gravel and the armored regiment would most diligently get every last morsel of flakes and other feed out of the gravel. I don't keep plants.

Even if ten of us said our holpos couldn't do it, which would form a rule, we know how amazingly different each tank can be and how our hobby is riddled with exceptions.

I agree with Mark too that the snails could be considered, even though neither have I ever dealt with them.

Could the sediment come from the filter?

Could have someone developed a taste for plant roots or what lives in the roots?

Might have substrate-dwelling creatures been introduced, like black worms?

Well, eliminating a few possibilities here...
--I don't think it's the snails. I've had them in all my tanks and I've never seen them dig at all, let alone move mountains.
--It isn't from the filter, although there is a lot of current in this tank, so it's obvious how it's getting blown all over the place.
--I don't see any plants dug up, although the dwarf sag in front is struggling, probably because it's burried most of the time. But now that you mention it, the cabomba in the back hasn't been rooting like it used to. This tank has been set up for a year, and dirted tanks tend to go through a transition around that time, causing certain plants to struggle and others to dominate. I just chalked it up to that, but maybe they are getting actively dug up.
--It's possible, even likely, that there are critters in the substrate, but again, that's the case in all my tanks, and none of them move mountains.

I'm not seeing any actual tunnels or anything, although there could be some back behind the boulders and driftwood. The surface does seem pretty stirred up, but I'm not sure where the deep digging is taking place.

Thanks for the ideas. Please keep 'em coming if any of this makes you think of anything. T

Haha, you made me chuckle, Thomas! Let alone move mountains

Well, from everything that has been said here, indeed I see nothing else to blame but the hoplos, especially if there is a possibility they don't get enough feed.

If possible, I'd at least temporary separate them out and observe if it makes any difference. Sometimes one must experiment. Not everything can be solved on paper.

Well said, Viktor. I think I'm going to have to just put them in catfish jail for a month and see if the situation improves.

Do pay attention to what Victor wrote about digging when hungry. You might want to feed them a bit more after moving

Bas Pels wrote: ↑11 Jul 2018, 07:55 Do pay attention to what Victor wrote about digging when hungry. You might want to feed them a bit more after moving

Yes. That has actually been an ongoing difficulty with this tank. Since it is not in my home, daily feeding is done by the office staff, so I have little control over how much food goes into the tank. I feed my tanks sort of by feel--feed, keep an eye on how much food is eaten, and adjust--and that is a difficult skill to pass on to someone else.

A further complication is that these rainbow fish are PIGS! They eat the flakes, the freeze dried food, the catfish pellets, and even hit my fingers when I go into the tank.

So, I suspect that not much food usually gets to the bottom.

WhistlingBadger wrote: ↑11 Jul 2018, 13:17 ... A further complication is that these rainbow fish are PIGS! They eat the flakes, the freeze dried food, the catfish pellets, and even hit my fingers when I go into the tank.

So, I suspect that not much food usually gets to the bottom.

That was my fear too but I didn't know much about feeding habits of rainbows. If they are that ravenous, it makes the "hungry hoplos" straw man proposal more solid.

I think this also explains the fact that my hoplos would work and clean every surface in my tank, while your plants remain covered by sediment - your hoplo must have found out that there is never anything edible to be found on the plants, rocks, and other surfaces but only in the substrate and below.

WhistlingBadger wrote: ↑10 Jul 2018, 22:40 ... I think I'm going to have to just put them in catfish jail for a month and see if the situation improves.

Haha! If nothing changes, they can get back out on parole. If the opposite, off they go to prison

OK, this situation with the hoplos is getting serious. I was able to catch one of these critters, then spent an hour cleaning off all the hardscape and plants on Sunday, and by monday it was all covered with sand and gunk again. This fish has hollowed out a huge cave under one of the boulders, and I suspect it has other hidey-holes too. Worst of all, I can NOT catch (or even see) this thing.

I tried netting it last time it was out in the open, and almost had it in the net when it suddenly figured out what was going on and vanished. I haven't seen it since. The gals in the office tell me it's alive and well, but even they rarely see it, and then only for a moment. It appears to have gone fully nocturnal after its big scare.

I've tried rousting it out of the caves I know about, and I've tried the old cut-the-top-off-a-bottle-and-reverse-it trap. No luck. I have GOT to get this thing out of here, but I don't think even draining the tank would do much good because it will just stay in its hole.

Any ideas?

Wow, that is something!

To reference an old saying, it's easier to bring Mohammad to the mountain than the mountain to Mohammad.

Either solve the frustration of the hoplos (why are they tearing up the tank?) or move them out of the tank.

Cheers, Eric

Yep. Just a question of how the heck to get the out of there!