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Hello I have a Rio180 with a classic 2217 external filter and looking it to be a pleco only tank.
So would it be possible to stock different L number pleco in the same tank. If so what do you think would work.

Water ph is 7.4

You should be able to mix and similar size species together in that size tank.

There are a few things to consider here:
1. Diet.
It's sometimes difficult to keep fish that have "diametrically opposed diet", e.g. herbivores with carnivore fish, because (most likely) the food for the carnivores will be eaten by the herbivores, who are not "built" to take that much protein and low fibre content in their diet, and thus will suffer "bloat" (internal infections).

2. Temperament.
Clearly, very territorial fish (e.g. ) would not be suitable companions with much less territorial and "spiky" fish.

Also, shy fish won't do well with very outgoing/brave fish, since the shy fish will not get enough food.

3. Size.
Fish that are of similar size will do better together than very large fish mixed with small fish. This is perhaps not quite as important.

4. Cross breeding.
You do NOT want to create hybrids, so keeping different species of unsexed or opposite sex members of the same genus (e.g. Hypancistrus or Peckoltia) is a bad idea.

The key here is to ensure the fish gets enough of the right kind of food, and that they don't breed between different species.

--
Mats

I have many different plecos in my 180 gal planted show tank, a couple of keys that work for me. First and foremost is do your homework and research. Some plecos are quite pricey and you don't want (trial and error) mistakes as not to deal with loss of life and not to mention monetary loss. Mats made some good points so also take heed to that. I have alot of driftwood in my tank making for many hiding places big and small. In my experience, ph is not that big of a deal in which you can make adjustments to slowly acclimate your fish to the level of ph from your tap, as long as its not exceedingly high, the hardness could be a slight factor but you can also adjust that via R/O water or peat filtering. Daily monitoring is also a key so you can remedy a problem before it gets to big. Good luck and enjoy.

MatsP wrote:
Fish that are of similar size will do better together than very large fish mixed with small fish. This is perhaps not quite as important.

This is not always true. Similar shaped fishes with a similar size can easily been seen as competitors while fishes that are a lot smaller are only, well, small fishes. And you can easily avoid fights for caves if they want/need other caves.

If you want to try this you need 2 species that have a big difference in adult size and of course you can't choose a fragile species as the small species.

Bijn had a good point and that is true in my tank, My plecos range from a 7 inch L240 to a 2 inch L027 with many in between,there is some competition for food but that is only natural and I monitor to make sure all get fed which means different feeding times. You can also have different species as juveniles together and if they get overly aggressive when they mature you can seperate them and by my experience this usually happens when the males come into spawning condition.Enjoy