I know pond water is full of lots of goodies that plants like, and I have often used it for outdoor plants, but lately I started using my greenhouse pond water to water seedlings and established plants in my greenhouse. I only take out 2-3 gallons a day right now and replace it with fresh well-water, the same water I use to top-up the pond after backwashing the filter 2x a month. I can see the gallon requirement going up as we approach summer to perhaps 6-10 gallons a day.

Does anyone see this as a problem, for the plants or the pond?

My pond is 425 gallons, planted with a miniature cattail, fake miniature bamboo, and a miniature lily. I have 5 medium (3-4") goldfish and a baby that is about an inch. I do not feed them. I believe in letting them earn their keep by eating algae, and they do fine.

In general, not a problem. The fish aren't adding anything to the water that your soil and plants can't handle. It should be fine as long as you're not putting additives in the pond (such as chemical algae remover). I water from my ponds all the time, but my greenhouses are all organic.

I use my 'used' pond water for my houseplants especially during winter [water shut off to shed during winter], seems to work fine.

Fish tank and pond water is perfectly fine for watering plants. Paul is right when he cautioned about chemical additives. Some even use salt in their ponds. I would not use that water.

And, you need to know your plants and what they can handle too. I grow Carnivorous Plants and they always need very low mineral water. Pond water, with its fish nutrients, would be terrible for them.

I think the nutrients have been beneficial for my greenhouse vegetables. I draw the water for my ponds from my well before it hits the filtration system. (Water softener and low pH Water treatments). The minerals don't seem to be hurting the plants. I don't get too crazy about soil as long as I am in the ballpark with it.

The year after I got our pH treatment filter. I watered all summer with that water. Couldn't understand why my plants were not doing as well, before it dawned on me that pH treatment adds salt. The salt was slowly accumulating in all the pots/containers in my greenhouse.