Yes, it was a 2nd hand tank which was emptied & refilled within a couple of hours using the existing filter & media etc. I then left it 2 weeks with various water tests before adding any fish. its now been another week & so was advised to do the 1st water change around now.
3 different LFS have advised that 10% weekly is whats needed so not sure why 50% would be required?
Tank is a Juwel Rio 125 with 5 leopard danio's & 5 harlequin ras currently.
Ok, sounds fairly reasonable to an extent.
Did you add ammonia to the tank, maybe 1ppm just to test if ammonia and nitrite will reach zero within 24 hours before you added your fish stock?
(This is the only real way of determining if the tank and filter is really cycled before adding livestock imho.)
I always advise new members to test with ammonia first (no livestock in tank), once you are satisfied tank and filter is cycled after seeing zero ammonia and zero nitrite but getting a reading of nitrate is normal, you then do a large a water change as possible, this is to get rid of nitrate in the water and give the new fish stock nice clean dechlorinated fresh water.
Try to add new fish stocking as soon as possible (within 24-48 hours is good) once tank is cycled and fresh water changed beforehand.
As for weekly water changes, I tend to recommend a minimum of 50% but preferably 75% of the total water volume.
Why?
These fish and other livestock have been using the tank water all week and the water will likely have a number of containments not least with nitrate (do remember nitrate is actually toxic to all tank stocking with the exception to live plants), so therefore that means the tank water and substrate will be dirty with poop and debris as well as the water having some containments which likely makes the water column to be fairly unpleasant for the tank stocking to live in.
So hence my recommendation to have the larger weekly water changes to help reduce nitrate to a low level as possible (especially if you do not have live plants) and to get rid of poop and debris in the water column, making this a weekly habit will help to strive for the best water and tank conditions you can give to your fish tank as the tank stocking will be more likely to thrive rather than just survive in old dirty tank water.
However with low tank stocking you can get away with lower weekly water changes BUT if you have overstocked on fish numbers or have species such as plecos which are basically poop factories and this will make the tank water become very dirty very quickly so therefore you will then need to increase water changes to a basic minimum of 75%.
This is not in your case at the moment but good to know for future references and for other readers to learn
