Hi - my tank is just under 2 metres. Exact measurements are 180cm length by 50cm wide and 60cm high. I work that out to be over 500 litres? In general I clean the gravel maybe once a week or once every fortnight and would like to know how much water I should be removing and replacing at the same time. I have 2 baby oscars as well as 3 blood parrots, 3 guaramis, 2 pairs of convicts and 2 angel. I do treat the water replaced with a de-chlorinator. Many thanks!

Very good question. In theory, you shouldn't have to do any more than the 30% water change once every week. However, as we know, many people often overload their tank with fish, When they do this, the nitrates get very high so you either have to do more than one water change a week, or a very large water change to reduce them to a suitable level.

So to answer your question, the amount of water you need to change will depends on how high your nitrates are at the end of the week.. I like to keep mine below 40ppm, Although many forums will lead you to believe nitrate levels are dangerous above 20, this is just scaremongering.. If at the end of the week, your nitrate levels are well below 40, you don't necessarily have to do a water change, just remove any crap that may be sitting in the tank.

Thank you for your helpful info - will try and organise myself a test kit through family or friends out of the country as we cannot buy them here. Went by gut instict before but I've just lost a male convict. I could not clean my tank for the last 2 weeks as our water was on and off and when it came back on, I didn't trust using that water. Obviously during this time, if I'd had a test kit, I would have seen what levels were up and could have made a plan! Having said that though, tank all nice and clean now and my new baby oscars are very happy and have settled in very very quickly!

The info OFL gave you is bang on. but i would add that someone wrote a good article about nitrates in tap water. If you haven't read it already give it a look cos your tap water is sometimes high in nitrates too, when you get your test kit check your tapwater to see whet you are getting... In any case it should be lower than that in your tank.

Marcus is correct, if you're finding that your nitrate levels are always high, check your tap water. I don't have any nitrate in my tap water, however I've read that people often have up to 40ppm of nitrate already in their tap water. So you can understand that some people have an up hill struggle when it comes to maintaining good water quality.

Thanks very much - this forum is a minefield of info! My water sometimes comes out white, when it does that - I leave the tank cleaning until another day. Never thought about actually testing my tap water before putting it in the tank, so thanks for that - hopefully have my test kit within the next month or so!

Don't worry, it may look like White water, it is in fact lots of air bubbles that make it look like White water. You'll also find that Cold water holds more air than warm water, so occasionally you may find that if the temperature of the water coming into your tank changes slightly, it will suddenly turn white, again, it's just millions of bubbles, completely harmless, do not it affect your tank maintenance.

Testing your tank water is the best investment you can buy, it will act as an early warning. I wish i had tested my water when i first started keeping fish, it would of saved me a lot of heartache and money. You will need Ph, ammonia, nitrite and nitrate. You can also test for hardness but it most cases this is unnecessary.

If your nitrates go over 40 you will need to do a water change. How much you will need to do will depend on how long you are going to leave it until the next water change, how many fish you have and how much you feed. You should only feed what they will eat in 2 or 3 mins, no more no matter how much they beg. Oscars are professional beggars

I am a bit overstocked so i do 2 water changes a week, a 50% and a 25%

Thanks hey for your help Don't think I've ever done a 50% water change, a bit less but usually once a week. A test kit will definately tell me if that's often enough or not. I find though funnily enough that a larger tank is easier to look after - I battled with a 1m tank but this tank close to 2 metres is a breeze! Have to wait though for my test kit and don't know what's on the market in South Africa, so will trust my husband to buy me a good one!!

I generally remove about 1/4 of the water every week and once a month I empty about a third. Due to the water restrictions in Queensland, I try not to change too much water when I can get away with it.

I have never lost a fish and have moved house with this 6 1/2 foot tank.

I only test PH levels occasionally and have never tested for anything else.....do I need to?

I have had the Oscars since they were about an inch and a half long. I think as long as you keep the tank clean and the filters clean then you stand a good chance of your fish surviving. However, I may have been lucky so far?

cheers

the only accurate way to know when to change your water is to test for nitrates. when your nitrates hit 40ppm its time to change your water. this will also determine the frequency and amount of water to change.

Testing only for PH is'nt good as this is the one factor that is not so important. By far ammonia followed by nitrites, then nitrates are the most harmfull. your PH can to some degree be a little off, and are more important if you are breeding. (or live in an area with poor PH for your fish) Ammonia and nitrites will kill or at least make your fish unwell and open to infection,as will nitrates but your fish can cope with upto 40% nitrates without harm. If you wish to keep your fish well please buy and test for ammonia & Nitrites, & Nitrates will tell you if to make a water change.(If over 40%) I think you have been lucky mainly cos you have kept your maintance up and filters in good order. Knowledge is better than luck,