It depends how much you use it. If you use it a lot then yes. If you don't use it a ton then you don't need it. however if it is outside then it needs chlorine no matter how much you use it.
swimming pool
To disinfect it.
Chlorine is added to swimming pool water to disinfect it.
It is necessary because the chlorine kills all of the germs that enter the swimming pool.
If your talking about Swimming pool its because your pool has chlorine in it and chlorine kills fish :(
chlorine
The swimming pool at the Landmark Hotel in London is 15-metres. It's a heated and chlorine-free swimming pool. One can enjoy swimming in this pool without worrying about the side effects of chlorine, especially if one is pregnant.
The liquid chlorine formula used for swimming pool maintenance is typically sodium hypochlorite (NaClO).
You can buy a skimmer at Target for about $12.00. I have a small 10ft. pool and it works fantastic
If the combined chlorine in a swimming pool is a negative number, it indicates a testing error or miscalculation. It's important to retest the water using a reliable pool water testing kit to get an accurate reading. Negative combined chlorine levels are not physically possible in a swimming pool.
Probably the chlorine. I doubt if chlorine is healthy for frogs.
the higher the temp the quicker the chlorine loss