Can I over do my water changes? I do about a 20-25% change twice a week but inbetween I still see bits of cricket and other little bits of food with white fur on them floating around waiting to be picked up by the filter and sometimes they dont. Is this white fur a healthy thing or is it not good? Should I vac them up between water changes? I am feeding twice a day now pelets in the morning and a cricket or two from my garden at dinner time. My Tiger Oscar is about 100mm long now is this to much food?

Your water changes are done to control your nitrates mostly. Obviously if you got little bits of uneaten food then you will have to just use a net or something if they are floating on the surface, or a gravel vac to remove them from the substrate.

Once your tank has been set up for a period of time you will get a good idea of how much water you need to change to control the nitrate. If it takes a 25% water change to maintain low nitrates then really, there is absolutely no point in doing an 80% water change.

What do you have got to bear in mind when changing large quantities of water if you may alter your pH dramatically very quickly which is not good for your fish. Obviously sometimes a large water change is necessary but this is normally at the beginning of an aquarium's life when your pH will normally be pretty much what is coming out to the tap. Many people find that their pH doesn't change dramatically

Also if you are getting white fuzz on food then you are overfeeding....obviously the food has not been eaten and is rotting in the tank....cricket bits hmmmm thats a first i see the exoskeleton of mealworms get pooped out but not crickets....do you have a big enough vacume cleaner??