It is exactly what you called it. "Slime". You should clean the filter media before this happens. Most successfull keepers of animals (pets) attend to the cleanliness of their charges/pets quarters and conditions very regularly and meticulously. My advice is to strip down and scrub the filter clean, and replace most of the media. Reserve some of the old media keep it wet and rinse it gently. This rinsed "old" media will innocculate the new clean media with the necessary bacteria to cycle the filter. Then service the filter regularly, keep an eye on the water quality in future and replace at least 50% of the water every week.
It's a protective coat that acts as a defense against bacteria, fungus, and parasites.
some type of algae.
I suggest that you learn more about your fish in your aquarium. One of your fish might be a bottom sucker which means that they eat all of the dirt on the side or bottom of your tank. If one of your fish are bottom suckers, that's probably the reason why your aquarium is clean. If none of your fish are bottom suckers, than somebody must be secretly cleaning your tank for you.
Yes. to be accurate These fish should be kept in an aquarium with a sandy bottom.
colourful tank.
Fishing in an aquarium; aquarium fishing is when you scoop fish out of your tank with a net.
The white film you are seeing is an overproduction of the fish's slime coat due to a crash in pH or infestation of parasites. The bottom sitting is usually consistent with parasites or bacterial infections, but being the skin is milky parasites are definitely suspect. To treat, raise the tank's salt concentration to 0.3% and add an antiparasitic medication to the water.
an aquarium
Aquarium as in fish-tank means "Aquarium"
A balanced aquarium in an aquarium that contains a full ecosystem. In a balanced aquarium fish will produce waste. This waste will be decomposed by snails, bottom feeders and bacteria, generally into ammonia. The ammonia is converted by two different strains of bacteria into nitrite then nitrate. Nitrate is then consumed by the plants in the tank. If all of the waste can be converted into nitrate, and all of the nitrate can be consumed by the plant matter in the tank, the tank is in balance. The balanced aquarium could be taken one step further to have the fish in the tank consume only the plant matter that grows in the tank. This will generally require a large size tank for the number of fish present, because it takes a large number of plants to flourish and also be consumed.
A balanced aquarium in an aquarium that contains a full ecosystem. In a balanced aquarium fish will produce waste. This waste will be decomposed by snails, bottom feeders and bacteria, generally into ammonia. The ammonia is converted by two different strains of bacteria into nitrite then nitrate. Nitrate is then consumed by the plants in the tank. If all of the waste can be converted into nitrate, and all of the nitrate can be consumed by the plant matter in the tank, the tank is in balance. The balanced aquarium could be taken one step further to have the fish in the tank consume only the plant matter that grows in the tank. This will generally require a large size tank for the number of fish present, because it takes a large number of plants to flourish and also be consumed.
Fish tank
I would assume some kind of polution and syphon off the bottom of the tank and do a massive water change.
You trasfer the shark and the glowfish to an established aquarium, and wait for the danios to help cycle the new tank until it's balanced, then you can put the others back in. If you're lucky, they may be able to withstand the cycling of the tank, but it will most likely shorten their lifespan.