I have a relativly new tank (started 4/9/10) that is 50 gallons and is cycled. I have a 1 oscar about 4 inches, 2 Silver Dollars about 3 inches, 1 Orange Severum about 2-3 inches and 1 pleco about 5 inches. Yes....I already know I will need a bigger tank and plan to upgrade.
In the mean time, I would like to know how often to do a water change. What is the purpose of doing a water change if all of your readings (ph, ammonia, nitrite, nitrate)are in the correct parameters? I feel like I should do a water change so I tested the water today and these are my readings since my last water change 2 1/2 weeks ago:
PH:7.4
Ammonia: 0ppm
Nitrate: 0ppm
Nitrate: 20ppm

Thanks for any help!

dcgonz wrote:


Best thing is to develop a 'regular' schedule...you want to keep water parameters consistent (consistently good, obviously) so a regular/consistent water change schedule maintains that. If you waited until the water becomes 'old,' and the readings start to rise--then you're getting a fluctuation of water quality... i.e. dirty water, clean water, dirty water, clean water...etc. etc. This fluctuation is not good for the fish obviously and can cause infection, stress, bacterial blooms, etc. etc. Regular Water changes are not so much to fix problems (although they certainly help when necessary), but to head them off before they occur. That's why water changes should be done on schedule regardless of good readings.


With your tank I would do 25% every 3 days , with the size of the tank and the fish load you're really gonna need to be diligent until you get the bigger tank, as even with one oscar in that tank by itself, nitrate levels are going to accumulate very quickly

johnny has given you a very good answer to question, so i will X2 it. the only think i will add is keep watching the nitrates, cos as the fish grow so will the nitrate level.

Wow...25% water change every 3 days...to me would seem to stress the fish out as well....that seems excessive to me. If my nitrates are fine do I really need to do a water change that often? Also, with that much of a fish load how soon do I need a bigger tank and how big of a tank?

The reason he is saying 3x a week is because of the amount if fish in such a small tank. The levels will jump very quickly. I had mine in a small tank and because they eat so much as babies - they poop a lot too ! Once I moved my fish into my 120 gal tank I only have to do my water changes once a week... check my levels twice a week though. I don't have any problems with the conditions now. The fish will get use to the water changes and it shouldn't stress them out too much. If it does stress them, it only lasts a few hours. (In my experience)

In case you didn't know... Craigslist has awesome deals on tanks! Got my 120 gal with oak cabinet and canopy with a sump pump for $200.

Even though your nitrate levels may remain low, other trace elements will build up without you realizing,. Also some minerals depletes over time which are then replaced by water changes. So it's good practice to get into a routine of carrying out a water change. If you don't have a routine is very easy to become lackadaisical when it comes to maintenance of your aquarium.

Yea I can definatly tell the difference in water after a change...I would say I'm OCD so being on a schedule is no problem. I was just wondering why water changes are necessary when water parameters are ok.

So...next question...when should I get a larger tank with the fish load I have now? It seems like the tank is empty with what I have now but I know the fish I do have will grow quickly.

dcgonz wrote:


It's really not that much actually, considering the small tank size. Shouldn't take long at all...if you get one of those 5 gallon buckets at your LFS it's only 1 3/4 bucket every 3 days. Or you could do 50% a week if you only have the time for one water change a week. Water changes shouldn't bother your fish too much...they get used to them if you have a routine, and they stay in the tank so there's no stress in having to remove them.

As to getting a bigger tank, I would recommend at least a 90 gallon for your oscar and the other fish, 55 would be the absolute minimum for just one oscar...and even then its pretty tight...(usually pretty snug in the width department when they grow--which is fast.) You might want to consider rehoming some of the other fish too. Plecos, if its a 'common' plec--the kind you usually find at your local store--can, and will, grow upwards of 1 foot and they are very, very messy.

When to get it?...the sooner the better, obviously...as soon as it's feasible.

dcgonz wrote:


You're fish will get used to the routine very quickly.
I often have to move the fish around by hand for they all tend to inspect my every move!
Not kidding. I can even throw in some pellets during maintenance and they go crazy to get them.

yah after a couple of times of doing you will be shoeing them out of the way because they will be be play with your hand in the tank. and i would look on craigslist to i only payed 60$ for my 120 it only come with the light and stand but i had everything else. you can get some good deals on there.

get the largest tank you have room for and can afford. you have started with a fair few number of fish so need as much room as you can get. you will only wish you got larger in a few wks if you buy to small. I would go 90-150g(uk) if you have cash/room. the larger the tank the less stress to the owner and fish an cleaning becomes easier as long as its not over stocked.

i would recommend stating with a weekly water change of 30%, but test your water for ammonia, nitrite and nitrate before a water change. If ammonia and nitrite are NOT zero then you have a problem with filtration (tell us on here and we will be able to help). If your nitrates are above 40 then you will need to do bigger or more frequent water changes(maximum in one go 50% or do 2 30% a week or more if needed). Remember test before each water change.

Remember to only feed them what they will eat in 2 mins and no more