This I learned when we visited my husband's cousin who has several big aquariums. The aquariums are being cleaned and my husband, upon seeing the unhealthy plants in the garden, said that the aquarium water is best for the plants instead of being thrown in the sewage. The cousin was surprised because he does the cleaning like that and didn't know that his garden would benefit from the aquarium water. Honestly, I also didn't know about it. My husband added that in some vegetable farms, they have a fish pond more for the water and not for the fish.
Your husband is exactly right, and the aquarium water would be wonderful for the plants, @Corie Henson ! My mother always had fish tanks, and put the used water on her flowers outside of the front door, and they grew beautifully. Some places have what is called aquaponics, which is where fish are being farm-raised, and hydroponic plants are grown in the water from the fish tanks. The water is then filtered by going through the plant systems, and goes back into the fish tank as fresh water. It is a great way to raise your own food, because you can have both the veggies and the fish , and it can be done in your back yard. This can be adapted to almost any size; so some people raise just their own food at home, and other places, it is done on a commercial scale.