Water changes for 90 gallon Oscar

First, a 90g is a pretty good tank for a single Oscar, but with a 48in footprint, not much room for anything else. While small, say 6ins or less, a single large weekly change, 75% or so will do. As the fish approaches the foot long mark, and obviously becomes a bigger strain on the bio filter, every 4-5 days will be in order.

A single large change is better than 2-3 of the equivalent volume, as nitrate is always being produced by your properly functioning bio filter. So, even 2 50% changes over say 5 days would not put you at the same level as a single 75% over the same period. Huge volume changes wont disrupt the cycle, and as for temperature, you just match the incoming water to the tank as close as you can. Couple degrees either way is no biggie.

75% a week for a single 6" oscar in a 90g?!

I doubt you'll need to do even half of that TBH. Change enough to keep your nitrates low, any more than that and you're flushing money down the drain IMO....

David R said:

75% a week for a single 6" oscar in a 90g?!

I doubt you'll need to do even half of that TBH. Change enough to keep your nitrates low, any more than that and you're flushing money down the drain IMO....

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I disagree.. there is more to water quality than nitrate levels. The fish excretes a growth inhibiting hormone thru their urine. Oscar is among the leaders in waste production, they urinate and defecate constantly. A 4ft 90g tank is not big for a fish that should grow an inch a month for the first 9-12 months of its life. Also, Oscar is among the more sensitive cichlids when water quality gets iffy. The cleaner you keep the water, the better the fish will do with color, size and longevity. A 6-7in Oscar is a bigger strain on the bioload than some fish of considerably larger size. Example from my own tanks. I have several Oscars of well over a foot long. Each of these fish produce VASTLY more waste than my male Jaguar of the same size.

suprd71 said:

The fish excretes a growth inhibiting hormone thru their urine.

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I know there is a lot of talk of this, and a lack of proper scientific evidence too, but obviously it does happen to some degree (thus why discus breeders do regular huge water changes on heavily stocked fry tanks). For a single small fish in a 90g tank I find it hard to imagine it would be an issue though. I know people say "more is better" in terms of water changes, so why not change 90% of your tank water twice daily? That's gotta be better than 75% every few days eh. You have to draw the line somewhere...

OP; your oscar isn't going to die if you can't/don't do 75% water changes every few days. If you want to do that (or more) then go for it, but I'm confident that you'll be able to keep it happy and healthy in that sized tank with a more conservative water change regime. At the end of the day it's your fish so you decide. Nitrate levels aren't the only reason to change water, but they can be used as an indication you're changing enough. If you keep them in check I'd say there's a good chance you're sufficiently diluting anything else too.

25% water change every 1-2 weeks would be more than sufficient. Where do you people get your facts from? The internet? Lol


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I do 90% once a week on all tanks


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