I am amazed that your frogs have survived this long. It is a testament of how hardy these frogs really are. You should do 25% water changes every other week whether the water is dirty or not. The "stuff" on the surface is not eggs or tadpoles. I would empty the water and thoroughly clean and sterilize everything. Once cleaned, rinse completely and put everything back in. Make sure your water is conditioned (I use Stress-Coat) and at the proper temperature, about 77(F).

Even if the water looks clean, it isn't. Also, since these frogs are aquatic, you will also need to look at the water chemistry. An inexpensive freshwater test kit will be helpful. As dirt and debris settles in the tank, ammonia, nitrate and nitrite levels begin to rise and that can be harmful to your frogs.