HOW MUCH WATER SHOULD YOU CHANGE IN A FIVE+ GALLON TANK WEEKLY?
The answer is ten to twenty five percent. However it does vary depending on the tank, your water, and how many fish and what kind of fish are in the tank. If the tank is very crowded you might want to change as much as fifty percent weekly. If you have a lot of messy critters in it like snails it will get pretty dirty. If you have one fish like a betta fish the water should be pretty clean usually. Just never change all of the water unless you have an emergency. Changing all of the water comes as a shock to the fish because the amount of bacteria changes dramatically. If the water becomes contaminated with disease, parasites, or chemicals then you may have to change it all. But only change all of the water if it is an emergency. I also recommend not cleaning the filter when you change the water. The filter still needs to be cleaned but it is better to do it at a different time because changing the water does get rid of good bacteria, so you don't want to clean the filter out right then because that would take out a lot of good bacteria that fights ammonia. Anyway, in another post I will get into changing the water more in depth.
Now for my favorite quiz question...
WHICH ONE OF THESE PETS DOES NOT EXIST?
The answer is the Peruvian Red Goldfish. I made that up. Yes a blue-tongued skink and a Jerboa do exist!! (and degu exists too but you all seemed to know that already)
So now you might be wondering what jerboas and blue-tongued skins are...
A blue-tongued skink is a lizard and yes, it really does have a blue tongue.
Here is a link to a picture:http://en.wikipedia.org/wiki/File:Blotched-Blue-Toungue-Alpine-phase.jpg
And a jerboa is a very odd looking creature. It looks like a cross between a gerbil, a kangaroo, and a mouse. Here are links to a page of information and a very funny video of jerboas (there are a lot of different jerboas. There is the pygmy jerboa, the long eared jerboa, and the five toed jerboa and more)