By Donnaj1dlh
Aberdeenshire,
Scotland 
My OH has been told by a fellow fish fanatic that fish tank water is good for plants as it's full of nitrates.... has anyone else heard of this .... anyone else use fish tank water in their garden??
23 Mar, 2011
Answers
Maybe I exaggerated by saying 'full' :), but the water certainly wouldn't harm the plants ...... maybe time to recycle the water then .... especially in the summer months :)
23 Mar, 2011
Donna - Love your optimism that it will be so hot a summer in Aberdeenshire that we will have a water drought :)
23 Mar, 2011
I would hope that you change the water often enough that it isn't "full of nitrates", Donna. There will be some nitrates in the water from when the fish poo and so the water will be better than tap water for plants, but |I would not have thought significantly so. If the tank water was "full of nitrates" it would go green with algae that would take up the oxygen, causing the fish to suffer.
23 Mar, 2011