how much Water change is required

Hi Every one I have read a few articles but all give a very vague answer i would like some more definitive answers if some one could assist please.

I have got a new tank BUT the water and filter media is old so the bio cycle should be pretty well established already, when we moved the fish in we moved the water substrate and filter also so it is pretty mature I think.

the tank is very close to 380l in size but I do have a few rocks and other decorations that will reduce the actual volume of water,

I have got

4x Blood Red Parrot (About 100mm size)
1x Clown Loach (About 150mm size)
1x Electric Blue hap (About 150mm size)
1x Yellow lab (About 50mm size)
1x Blue Peacock (About 60mm size)
1x Small Frontosa (About 70mm size)

I may have the bottom 2 switch I still dont actually know what fish they are but those are the sizes. I am feeding twice a day with a level measure approximatly 60mm diameter of Cichlid Gold

is there anything else I need to mention to get a better answer on how much water change I need to do and how often.

I have read mostly that 10% a week will be sufficient but please confirm

 

10 % weekly is a bit low IMHO. Personally I do 30 % weekly but I have much smaller fish and many plants in my aquariums. I would be aiming for about 50 % weekly if I had such a large bio load in my aquarium. Possibly even more, just not all in one go.

 

Wow as much as that,

okay so the idea would be then to do like a 25% every 3 days

 

Not if you are only doing 50 %. maybe 2 x 50 % a week. That doesn't equal 100 % WC though. As long as you can keep the nitrates in the acceptable range (I work on below 20 ppm) you should be fine. My experience lies with much smaller, schooling fish. Lets see what someone with experience in similar size / type fish has to say

 

as with my pond I should do a ammonia, nitrate, nitrites and pH test weekly right

 

Doesn't hurt. Personally I hardly ever test for any of those. I think its more about maintaining a routine that works for you and is healthy for the fish

 

water changes are relative to amount of nitrates in the water, ideally ammonia and nitrites should never show up. best way to work out how much and how often is to get a test kit for when you start a new tank.
To give you a example i have a 1600ltr tank set up with 9 large fish that I do 2 35% water changes on a week and 2 700ltr tanks with a single linked filter with 1 large fish in each tank that i do a 2 50% water changes a week on.
So no fixed cookie cutter option, this many ltr this many fish equal this much water to be changed, only way to know for certain is to test. More in general is better especially as now that it is warming up