Is it ok to add hot water to a tank to raise the temprature ?

I have a smallish tank and it dosent get very much sunlight. Theres light coming into the room but not directly on it. The water reaches around 16 degrees each night. Its housing 3 small baby yabbies or also called crayfish, and they grow bigger and faster if the tempratures between 25 and 30 deegrees. I would... show more I have a smallish tank and it dosent get very much sunlight. Theres light coming into the room but not directly on it. The water reaches around 16 degrees each night. Its housing 3 small baby yabbies or also called crayfish, and they grow bigger and faster if the tempratures between 25 and 30 deegrees. I would only add a glass of hot water now and again with the clorine remover of course, is that ok ? or would there be better ways other then buying a light.
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