your fish have a funus growing on them that will kill them go to aquarium and buy white spot and fungas medication. remove fish from DIRTY tank. clean tank. medicate the water. if fish are sharing tank with other fish keep them separate and medicate till whits spot is gone this fungus will contract to all other fish if let go is mostly brought to tank by introducing plants or other fish that have already been contaminated.also by a DIRTY tank
This is going to depend on if the black spot was part of it's colouring when you first got your fish, or if it appeared at some point while in your tank, and went away at some point after you did a water change. If it's the second part, then that would be an ammonia burn which is caused by poor water quality in the tank.
Hey there, i used to work in a aquarium and ill tell u that 80% of aquariums tell u to keep ur fighter in a bowl. But realisicly the are much happier in a heated tank (ive seen the proof) U can have a bit of water movement from a filter if u decide to put one in. But i wouldn't get a high powered one that's gonna blow him away. Just make sure u have some type of area where there would be less movement like a large patch of live plants or a hidey hole. Bettas come from Thailand, they are found in slow moving streams or even in shallow puddles along side the stream. Just thought i would say that :oD
Too much sunlight on the tank!!