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Alright so I currently have a planted 15 gallon with 13 Neon Tetras, and 7 very happy corydoras trilineatus. I like otos and wasn't able to get any when I first set the tank up. Now is a good time, as I've got a lot of the soft algae on my plant leaves and back tank wall. The kind of algae that you can just rub off with your fingertip. From what i've seen otos will eat that stuff up. I am also prepared to give them vegetables and algae wafers when they run out of algae.

Anyways, as for the question. AQadvisor has my tank currently at 91% stocked. I played around and added 3 otos which puts it at 107%. Most people say AQadvisor is very conservative with their estimates and you can overstock without issue. I am also getting a lot of conflicting information about how many otos make a bare minimum for them to be happy. I see a lot of people with just 3, and they seem to do fine, but I also see people recommend 5+. I have also seen pictures and stories of otos and cories getting along well, is it possible if I got just 3 otos they wouldn't feel so lonely because they could hang out with my cories?


How many otos can I get for my tank so that it is not too overstocked, and they are still happy?

I would consider 23 fish 1-2 inch in a 15 gallon tank HEAVILY stocked. That said the true carrying capacity of any tank is determined by water quality much more than stocking density. Assuming the tank is fairly heavily planted, it has a strong filter in good condition, and you are religious about conducting frequent large water changes... you should be fine.
-Shane

Have you got a pic of the tank?

What is the footprint? (length & width, not height) - I prefer to work out stocking density against surface area

I have both Otocinclus and Hisonotus and I don't think either one works well with the traditional fish length vs volume/surface area methods of stocking calculation, and in fact the majority of small fish dont.

Virtually all my fish are oto size or smaller and so I prefer to judge stocking levels by different methods:
Do they physically fit (all fish, not individually)?...the fish are in different niches and not overcrowded.
Are they compatible?...no issues with the mix, same water requirements.
Is it maintainable long term?...are weekly nitrate increases ~<20ppm? Will food be suffient?

I believe only the nitrates and food are likely to be concerns as its a classic mix without clear problem species.
Nitrates are easily tested and I feel if you need to do more than 50% water changes and have +20ppm nitrates a week then even if space allows the payoffs may not be worth it, however I don't see this being the case here as the numbers and tank size are appropriate.
Rather its long term feeding that's the problem. Whilst algae may be abundant now it it may not be sufficient to feed a huge number of otos over extended periods and not all will eat tablets or wafers. Thus I would start with a relatively small number, probably 3 (not less) and see how they do. Add another 3 in a few weeks if they do well. It can be tempting to squeeze in too many in order to make them more visible (increased numbers will also increase boldness so double positive) however more mouths means more food and you can't simply throw in extra flake, granules, wafer etc and watch them eat as yoi do with most fish. If they eat only from plants and food is on the substrate then they can still starve (I have 2 of 5 who eat from the floor, the others do not. Conversely my Hisonotus 'niger otos' spend lots of time down low).

Beware that buying otos can be fraught with problems. Don't impulse buy unless you trust the shops quarantine procedures. Disease isn't an issue but they don't travel well and so you want to be able to buy decent fish without a huge loss rate. Full stomachs and feeding in the shop tank is a good sign. If the shop does only limited quarantine then watch over 2 or 3 weeks to ensure you are getting a 'survivor'.

Good new is if treated well they can be pretty solid fish despite a reputation of being delicate and fragile and having a high loss rate.

That shows the stocking level with 3 otos, and the footprint as requested.

http://youtu.be/5vljUTS7Qms

There's a video of the tank. The plants, especially the swords have all grown in much more densly since that was taken. There are a lot more broad leaves for the otos to hang out on. I find my cories lounging on them frequently, which is adorable.

I will probably also buy more plants, or a piece of driftwood when I go to pick up the otos.

Alright so unless anyone sees any red flags with my setup it looks like I am going to go get 3 little otos in the morning! I am excited.

Looking at your fish list, I wold consider Corydoras trilineatus a bit large for the set up. Were you to change them for C cochui (spelling could be incorrect), which grow to only half their size, the whole plan would be feasable.

Half the length inplies in case of the same bodyshape 1/8th of the mass, and therefore 1/8th of the needed water. C cohui is however somewhat more filled, so I would say not 1/8th but 1/6th.

That would make a school of C cochui take the same amout of water as 1 C trilineatus

Hi all,

Barbie wrote:I personally think the tank is overstocked. If you simply must have that many fish, buy a bigger glass box for them.

I'm with the others, I wouldn't add any more fish and I think are a bit big. I also wouldn't add to a bare, "clean" tank, they really need high water quality and a fully established tank with some biofilm etc.

I think you might struggle to find , but is a nice small that would be available and behaves like the larger species.

Barbie wrote:While nitrates being low will be important and extra plants will help with it, you're going to struggle to maintain enough oxygen in the water overnight while the plants are also utilizing it. The only indication that you're having a critical issue is going to be corpses when you get over the threshold.

This bit I don't agree with. It is often quoted, but it is based upon a series of, understandable, misconceptions.

If fish die in a planted tank from the combination of high CO2 and low oxygen levels this will always occur at night, and plants respire at night using oxygen and producing CO2 which leads to the obvious conclusion that oxygen use by the plants has killed the fish.

So far, so good, but in an un-planted tank the same high CO2/low O2 scenario and fish death can occur at any time of the day or night, because the biological filtration system is entirely reliant on microbial nitrification, and biological filtration is an oxygen intensive process.

The major difference is that biological filtration by "plant/microbe" systems has potentially at least x10 as much biological filtration capacity as "microbe alone" systems. There are a number of reasons for this, one is negative feed-back where higher CO2 and nutrient levels (particularly N (nitrogen) and K (potassium)), lead to increased plant growth, with the extra carbon (C) and macro-nutrients being removed from the water column, and incorporated into the plant tissue.

One of the other major areas where plants make a large contribution to a positive oxygen balance is in the substrate. Here plant roots produce large zones of biological activity in the rhizosphere, the zone surrounding the root. The plant is, both actively and passively, leaking nutrients and oxygen into substrate, supporting a large microbial biomass. Obligate rooted aquatic plants have special vessels in their roots, stems and/or petioles called aerenchyma, who's role is to conduct oxygen to the root zone.

Another reason is what happens at the end of the photo-period, when both tank water and plant tissues are fully saturated with oxygen. These factors mean that oxygen usage by the plants through respiration is lower than would be predicted, and the high starting level of oxygen leads to higher levels of dissolved oxygen than in un-planted, or lightly, planted tanks.

Because of this, rather than plants being the "smoking gun" of fish death, the fish would actually have already died without the plants.

cheers Darrel

being as generous as possible on stocking density, in a 24x12 you are overstocked with corys & neons.
I agree with all said above re: stocking, alternate cory species (habrosus & pygmaeus would be great or maybe aspidoras if you can find them) & with otos needing mature tanks with biofilm etc.

Hi all,

Barbie wrote:So the end result would be dead fish from overstocking at night, correct? While I realize I simplified the situation, it really isn't going to change the fact that the tank will crash, is it? Thank you for the explanation, but it doesn't change my recommendation. Still too many fish, regardless of what else is in there.

Point taken, I don't think any of us are arguing that adding the to the tank is a good idea, and I agree that fish death is most likely to happen at night in planted tanks, and that once fish death has occurred, due to low oxygen levels, the extra ammonia produced is likely to lead into a positive feedback situation of further oxygen depletion and further death.

The point I really want to make is that plants aren't the problem, they are at least part of the solution.

cheers Darrel

Why not upgrade to a 20 gallon? if this were a 20 gallon, I would say, I think you might be able to get away with your proposed fish stockplan. However, 15g is probably too small for any long term success with the proposed stocking plan. I would upgrade to a 20 gallon, plant heavily, wait 4-6 months until it is fully established with you current fish stock and the plants have time to grow out nicely, then and only then should you add the 3 ottos that you want. This would work. I have a 20 gallon that is heavily planted and successfully running for 2 years with 5 otos, 6 cory catfish, 6 guppies, 10 neon tetras. Notable mentions: a strong filer is required for this setup (I run an Emperor 400), a bubble maker/power head that runs at night for water surface agitation (very important with the suggested fish/plant combo) and weekly water changes of at least 1/3 water volume. Good luck!