Flow rate suggestions for continual exchange tank.

I've got myself 6 discus that are about 7-8 cm long, a bit smaller than I wanted. They are in my 6x2x2, with a heap of other small fish, on a continual water exchange system. I need these fish to do some serious growing as they are stunning IMO and I want to pump them as hard as I can in this tank.

My question is how much water do you think I should be pushing through my tank?

I have enough bio filter to support a small whale :) And I'm thinking that the stocking is very low for a grow out tank?? The system holds about 800 litres max, including the sump and I am currently exchanging about 400 Litres per day. Its bare bottom and crap does not accumulate. I've got plenty of time on my hand at the moment, so these fish are pretty well going to get fed as much as they can eat, many, many times per day. The other fish in the tank are looking fat from the scraps alone.

How should I manage this? via nitrate readings?

Oh, a heap of small fish means 6 rams, 30 cardinals, 15 cory's and 6 bristlenose

I thinking 6 baby discus should be in a smaller tank without tanks mates. Makes the whole grow out pocess a lot easier. In all likely hood they will grow bigger and healthier without other fish or plants in their tank. And may even feel more secure in a smaller.

Makes sense, I'm kind of stuck now though. There's no plants or anything to trap detritus and stuff, the bottom stays very clean. Now i'm trying to convince myself LOL.

Thanks for the advice

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Originally Posted by bluelagoon

I thinking 6 baby discus should be in a smaller tank without tanks mates. Makes the whole grow out pocess a lot easier. In all likely hood they will grow bigger and healthier without other fish or plants in their tank. And may even feel more secure in a smaller.

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I've been thinking about this and although your it's clearly best practice, I'm not sure that I understand it fully.

Just to be annoying and run a hypothetical argument against it. - Small fish in a large body of water will experience much less fluctuation than the same in a large tank. The other fish in the tank don't add much bio load to the tank as they are only eating the scraps of the messy discus. My new discus have already enjoyed the company of their companions in the form of 1 meal of ram eggs and 1 cardinal tetra for a snack. It appears that the friends make them comfortable in a large space. My tank is minimally decorated, bare bottom. Nothing piles up on the bottom, the solids filter gets swapped out once per day and I can push as much fresh water through it as I like buy opening a tap. I am treating it as a discus tank while they grow, the other fish will have to deal with whatever the discus want.

Would I still be better off in a smaller tank, without friends? Given that I'm not concerned about excessive water changes, loss of a few minor fishes and running a bit inefficiently.

You're fine unless your goal is the absolute largest potential fish.
I get to 6 - 7" without issue doing similarly

6 to 7 inch fish would be just fine, I hope I can do it as well as you have. Thanks.

A bigger tank will need just as much maintenance as a smaller tank during grow out, maybe more. The amount of food and waste they produce at a young age from eating numerous times a day will make a smaller filter and tank a lot easier for maintenance. Discus are very dirty fish (but beauiful) and shed the slim coat continuously. The glass will need wiping down more often than most other species. With other fish in their tank, it's just compounding the clean up at a time of heavy feeding. Some emphasize the trick is to start them in smaller tanks to restricts their movement and calarie burn; then when about 4 inches move them to a larger tank. On the other hand, I would put 12-15 discus that size in a 6 foot tank and no other fish until about 4" if I was to go with that size tank to make it all worth while,altho IMO not the best choice.

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Originally Posted by bluelagoon

A bigger tank will need just as much maintenance as a smaller tank during grow out, maybe more. The amount of food and waste they produce at a young age from eating numerous times a day will make a smaller filter and tank a lot easier for maintenance. Discus are very dirty fish (but beauiful) and shed the slim coat continuously. The glass will need wiping down more often than most other species. With other fish in their tank, it's just compounding the clean up at a time of heavy feeding. Some emphasize the trick is to start them in smaller tanks to restricts their movement and calarie burn; then when about 4 inches move them to a larger tank. On the other hand, I would put 12-15 discus that size in a 6 foot tank and no other fish until about 4" if I was to go with that size tank to make it all worth while,altho IMO not the best choice.

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I don't know how anyone finds that enjoyable... Everyone is obsessed with size.

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Originally Posted by slicksta

I don't know how anyone finds that enjoyable... Everyone is obsessed with size.

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I don't understand what you mean by that.

I think slick is saying that fattening fish in a bare glass box with a sponge filter is more like work than play, compared to growing them in more aesthetically pleasing tank.

Everyone gets something different out of fish. Some like pumping discus to their max, others like aesthetics. Each to their own.

It sounds like I'm not going to grow giants, but should still be able to produce nice fish, That'll do for me.

I think you can do it. I might suggest slowing down the flow rate during feedings so they can eat before it goes into the filter. That's what I do in my reef tanks.

Assuming you don't have a denitrator in your system then nitrates are a proxy for the bioload materials that accumulate. Use nitrates to determine the amount of water you need to exchange, many aim for <10 ppm.

I think the other reason for the small tank is that the cramped environment up's the competitive cichlid behavior of discus making them more competitive for food. Often times for grow outs more juveniles than can be accommodated in the final tank are purchased as there are invariably ones that don't grow as well or don't color up as nicely for the final 'display' tank.