Tried answering this earlier but Google ate it.

The tank is 1.8 gallons and we've had it for about 4 weeks. There are
only two Zebra Danios and two silk plants in it. There is an under
gravel filter, bubble wall and a SpongeBob that came with it. The link
is

http://www.wonderfullywacky.com/spongebob-aquarium.htm

Someone on this list suggested that I add more gravel because it barely
covered the bottom. (They had one so they knew right away what I had.)
I did this when the tank was 2 weeks old.

I tested the water with a Master Test Kit

http://shop.petsmart.com/product/253...4441776772.htm

Thanks,
Kay