Real and final tank size for Rhom

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Piraka

Feeder Fish
MFK Member
Jan 5, 2025
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Hey everyone,
I’m new to piranhas but doing research for eventually getting one.

My favorite is the Serrasalmus Rhombeus, by looking in the Internet and checking out people’s setup I see very different info on tank requirements for an adult.

Some people say 120g is enough, others say 180 minimum, Seriously Fish even says a 2 meters long is the minimum required.
I just would like to know what’s the actual size of the tank required for him to be well for life.

Knowing I would not get a monster 16 inch but I would like a baby 3 inch for him to grow and stay with me for all his life.

Somebody who has them can clarify once and for all what would be the gallon capacity and size of the perfect tank for an adult full size Rhom raised in captivity ?
thanks !
 
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In these sorts of threads, the answer that is least what you want to hear is usually the closest to the truth.

Before buying and setting up my 210 Frontosa tank, I researched piranha extensively. In almost all cases, the answer came back that it’s most recommended to get a 6 foot tank for these guys - even the ones that can only be kept solo.

For me, dedicating a tank that size to just one fish seemed a bit boring - so I went in a different direction.
 
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That is, 700 liters (200 gallons) would be the bare minimum, in truth ?
Besides the fact that if people respected that almost nobody would have a Rhom, but in the fish’s wellness perspective
 
15 inches, in a 180. Keep in mind it’s not just size of fish, or tank, but also how dedicated one is to water quality, and filter maintenance. Let that slip, and the increased bacterial load from waste results in stress, which with this species will manifest in chronic HITH - which is what happened to the RHOM in photo below that was owned by a local fish keeper.

1737725914626.jpeg
 
That is, 700 liters (200 gallons) would be the bare minimum, in truth ?
Besides the fact that if people respected that almost nobody would have a Rhom, but in the fish’s wellness perspective

I don’t know - 6 foot tanks can be anything from 125 to 210/220.

Lots of people seem to keep them in 180s. I’m not sure about the 125 - might be a touch small.
 
I would say buy the tank the biggest you can if people say a 125 is good but you can fit a 180/210 in your place then get the biggest tank you can.
 
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I would say buy the tank the biggest you can if people say a 125 is good but you can fit a 180/210 in your place then get the biggest tank you can.
That’s my point, I think 125 is my max and as much as I would love this fish I will not get it if it’s not good enough for him.
And I don’t know if I can trust the internet because many people do keep it in 125 but I don’t know if they do just because they cannot have more and they prefer that to not having the fish at all, at the expense of the fish being too big/active for that tank
 
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If the 125 is the biggest you can get there are other fish to think about. Your willing to donate a 125 gallon to a single Rhom then why not look at Red Devils, Midas, Jags, Red Terrors all those fish actually have more personality then a Rhom IMO
I'm not sure of the growth rate of a Rhom but you said you wanted a 3in fry maybe try it after a few years if the fish is struggling or you cant stay on top of maintenance then sell the Rhom or trade him
 
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That’s my point, I think 125 is my max and as much as I would love this fish I will not get it if it’s not good enough for him.
And I don’t know if I can trust the internet because many people do keep it in 125 but I don’t know if they do just because they cannot have more and they prefer that to not having the fish at all, at the expense of the fish being too big/active for that tank
The Rhom is a very slow growing piranha species the 125 should be good for years. I personally have kept a small black rhom and kept redbelly. The redbelly growth was much faster imo.
 
The Rhom is a very slow growing piranha species the 125 should be good for years. I personally have kept a small black rhom and kept redbelly. The redbelly growth was much faster imo.
thanks !
I believe I would start with the max size tank from the start rather than trusting the future me to be able to upgrade the tank after x years 😅
I guess if 125 gallons is not big enough for a Rhom for life, I would not get it and look for a different Serra :(
 
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