A 25% water change will only reduce ammonia levels by 1/4. This means that unless you had a barely detectable level (such as 0.1) to start with, you'll still have quite a bit of ammonia in the tank.
P@H recommend small water changes for one of two reasons (depending on which sales assistant you talk to):
1) There is bacteria in the water. This bacteria cycles your tank. Large water changes reduce the bacteria and should be avoided.
This is false. Yes, there are bacteria in the water but
not the ones that cycle your tank. The right bacteria for cycling are found on the filter media and occassionally on other surfaces in the tank, such as gravel and ornaments. Doing large water changes will
not remove the essential bacteria.
2) If you do large water changes, you'll remove this ammonia. This is good for the fish but will make your cycle happen really slowly. The damage done by elevated ammonia isn't severe enough for a slow cycle to be a good trade off.
This is also false. The bacteria can only use as much ammonia as they can use, right? And they're always growing and always eating. So, if there is excess ammonia in the tank is it because the bacteria
can't use it yet. The ammonia
is highly toxic to fish and all suffering to the fish should be limited or eliminated. You can happily remove the excess ammonia as much as 2-3 times a day and still cycle your tank.
Most sales assistants at P@H know sweet F-A about cycling and those who do know their stuff are actually limited by company policy to give certain, company approved advice.
If you have ammonia present in your tank you need to test the water twice a day and alays do a large water change if you have a detectable level of ammonia. You always want the test to read zero and remember, a 50% water change only reduces the level by half. So, you could well need to perform 1-2 75% water changes a day just to keep the ammonia down. This is hard work but it is essential to keep your tank healthy. P@H will not tell you this - if they make fishkeeping seem too hard and if the fish the customers buy are too healthy, then they lose money. They want you to overstock your tanks, lose some fish in the cycling phase and buy lots of products (such as treatments and "bottled bacteria").
You need your own
liquid test kits for ammonia and nitrite as a minimum to get your fish safely through a fish-in cycle (which is what you seem to be in). Here is our
Resource Centre which has information on fish-in cycles, cycling in general and loads of other essential information that you just won't get from most pet shops.
Good luck!
