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i have heard that the pygmys (dwarf) corys dont spend too much time on the bottom, and they actually like to swim in the lower middle regions of the tank...i have a 70g planted tank with leaf litter/pea gravel bottom, the species i have as of now are a school of 14 Serpae tetras,a pair of Splash tetras, and Apistos...my ph is 6.0....i wanted to get a large school of pygmys but dont know if they would be doing their normal 'corey' scavanging/hiding underneith the leaf litter bottom kind of behavior...any information on them would be great!

thanks
dan

danpbmx,

Firstly there are more than one species of so called dwarf Corydoras and only one of these prefer to swim in mid water, this is C. hastatus, which is often confused with C. pygmaeus. Both species graze the substrate as well as plants and any other tank furnishings in their serch for food particles.

'corey' scavanging

Cory's are bottom feeding fish not scavengers and should be treated as such to get the best from them.

Pea gravel in my opinion is a definate No No for any tank that houses fish, food particles will penertrate well into the gravel and out of reach of most fish, where it will decompose and be the start of major problems to come. Cory's are not built to move large pieces of gravel, in the main they are more familier with a sandy substrate, which they can filter through easily. Dwarf Cory's would more than likely to get trapped trying to reach the particles of food.

Leaf litter is good and natural providing the leaves are none toxic, Oak or Beach leaves are OK.

Ian

pea gravel is actually better than sand in my opinion, when using sand with plants the roots of the plant usually decompase and spoil underneith the sand, i have used sand for a while and in my opinion is horrible for planted tanks, it is not a good substrate in the long run...second, they are beach and oak leaves...i know coreys are not scavengers, i meant 'scavenging around' as in looking for food...and since you say that pygmys will get lost, would you prefer a larger species of cory...?

danpbmx if you can get the right type of sand, one that doesn't compact then you probably wouldn't have the problems you have encounted. Corys do much prefere sand to any gravel.

Dan,

OK may be I misenterpreted your 'scavenger' comment but large gravel in my opinion is not an option for any Cory tank and for that matter it is not the ideal substrate fo plant roots either. fine gravel or sand is, all Cory's large and small sift through it, I have Sand, 8 -10 mm deep, in most of my tanks, it is fine river sand, the particles are rounded like tiiny pebles, this type of sand does not compact and allows movement of water through it. I also have plants, some in pots and some growing on pieces of wood or rocks.

I think the thing that needs to be decided is which is the priority, fish or plants. If you want to have a large shoal of C. pygmaeus then I would sugest that they should be the priority and given suitable conditions, otherwise if you introduce them into the existing set up they will very soon start to suffer and die off. Even with one of the larger Cory species, if they cannot move the substrate to get at the food particles then you are still likely to get gravel polution problems. The other problem with Cory's and Plants is that with their constant foraging plant roots will be disturbed, which does not help plant growth.

Ian

hmm, my 'pea gravel' is pretty small, i dont know what you guys are considering 'sand' mm. wise, but i know plenty of people with discus tanks with gravel and huge schools of corys and they do fine...it sounds like this is the extreme, sand, but im sure plenty of species can survive with gravel...and i would like to see this 'sand' that dosent compact, it must not be sand then...

You said it yourself

survive

are recomendations are what would be best for the fish.
Why do you think if it doesn't compact then it must not be sand, the difference is in the grain shape, sand that is not prone to compacting has round grains, simple.

By definition pea gravel is the size of pea's. Diamentions would be between 6 and 10 mm diameter. I concider fine gravel to be 1.5 to 2.5 mm diameter. Sand can vary from .o5 to .5 mm diameter.

What is the average size of your gravel? and what method of filtering are you using?

In your original post you were seeking advce to which several of us gave based on our experiences, in my case some thirty years. Most of this experience being gained the hard way, by trial and error. What I have said about the merits or pitfall of sand and gravel is based on all my experiences. I offered my advice as a guide based on your question and not as a point to build a lengthy debate on. Listen to the advice, decide for yourself if you want to acept or reject it, then see what the results are based on your decision, but if you really want to learn from the exercise make notes of what you do. You'd be amazed how much more knowledge you gain and you have a record to refer to at a later date.

Ian

Well, all I can say is that the various species of Corydoras I've collected in the wild none were living on pea gravel. Or, for that matter, were there very many plants around (in the water) there were plenty shading it. Having said that I have found them living over rock chip gravel so sharp I couldn't walk on it.

That said, I keep Corys on pea gravel and, in other aquaria, sand and I have better plants in the gravel tanks and slightly happier corys in the sand I feel. If you are going to use pea gravel in a cory tank then I'm of the opinion that you use UG filtration. Wih sand you can use anything else. I guess it boils down to if you are more interested in cosmetics or fish "happiness".

Jools

undergravel filtration is a no no with planted tanks, why would you need to use them with corys?...Coryman, i have 'fine gravel' then, sorry, my gravel is much smaller than peas, but over here we consider pea-gravel, gravel that is smaller than normal...i wouldent see a problem with corys not being able to find food...

danpbmx wrote:undergravel filtration is a no no with planted tanks, why would you need to use them with corys?

That's a bit of an aquatic urban myth; if you use 4 inches or more gravel and you're talking about at least a four foot tank then you can actually have a planted UG filtered tank. For beginner's up to intermediate aquarists this is actually quite a good idea for groups of corys as they are much less prone to barbel loss over UG filters than they are otherwise. Of course substrate comes into it but, IME, barble loss happens much more often because of poor water quality than inappropriate substrate.

If you are going to be as diligent with water changes and filter maintenance as Coryman is, then you are best keeping corys over sand and that precludes UG filtration.

Jools

Dan,

undergravel filtration is a no no with planted tanks

Is this a statement of fact or your opinion? sounds like a reply from someone that knows all the answers! Instead of just making a statement quantify it and tell us why UG filtering is a no no for plants.

Ian

let me jump in here for a minute. i agree that planted tanks should not have ug filtration only when you are dealing with plants that are root based, like the Echinodorus or Cryptocoryne species. their roots, similar to trees, don't just stop going down just because you want them to. what happens next is not so hot. the roots go into the ug filter and disturb the bacteria. It is ok with stem plants that get their nutrients mainly from the leaves.

now, there are many different types of filtration to use, and not all include mechanical types (none in nature). there is one that could help you make the best of both worlds. get the river sand, as recommended, and either put potting soil (make sure it is completely organic. no extras in it whatsoever) and put the sand over top. the roots of your plants will start heading to the bottom to the soil (which as it decomposes, gives you a bit of co2 for your plants ) and the sand keeps your corydoras happy. and you could use whatever filtration you decide, b/c the plants will act as a natural filtration system, sucking up the nitrogen in the water, along with other metals your fish would prefer to never see! i did not make this stuff up.

i did not make this stuff up.

So would you like to explain how:

the roots go into the ug filter and disturb the bacteria.

after reading pg 127 of "ecology of the planted aquarium: a pratical manual and scientific treatise for home aquarists" by diana walstad (edited by Echinodorus publishing, chapel hill nc, usa) and published by , maybe the root thing was off, but by my experience, swords (Echinodorus) do grow big enough to cause problems. but here is the other, more scientific reason as to why. and i am typing verbatum.

the substrate may be too 'aerobic', because the undergravel filter circulates oxygen-containing water constantly throught the gravel. micronutrients like iron stay 'locked up' in their oxide precipitates, which plants cannot use.
while some hobbyists report that their plants grow in older tanks with a ugf, this is usually because some mulm has accumulated underneathe. water is no longer flowing evenly across the fulter plate, but 'channeling' inbetween pockets of mulm. plant roots find the nutrients and anaerobic condition they require in these mulm pockets.
without a ugf, pure gravel subtrates inevitably collect organic matter, become anaerobic, and release numerous toxins. a ugf keeps the gravel aerobic, so that it actually becomes a biological filter (nitrifying bacteria colonize the gravel). this is why undergravel filters work so well in 'fish-only' tanks.


so, unless you want to use soil as substrate only, which could be conducive for corydoras, but would cloud that water, the only option is sand. and as we know, sand would not be able to stay from between the grates in the filter. thus, negating the whole idea of plants and ugf.

maybe the root thing was off,

that was all you needed to say, and i agree to some extent the drawbacks conserning undergravel filters and plants.