This one's going to be unusual, I guarantee!

[funder_memphis]

First - I've built and tended to a 29 g planted indoor aquarium for 5-6 years now. It's very heavy on plants and light on fish; therefore, it's quite low maintenance. I'm not completely clueless about planted aquaria, but my "low input" tank is the only one I've really designed.

My situation: I have three horses in a small field with a 200-250 g round watering trough. I got really tired of dumping the tank and scrubbing algae every weekend, so I decided to treat the trough like a giant aquarium.

I selected really hardy stock, all "captive bred" in my parents' water gardens. I got a 5 gallon bucket of anacharis and water lettuce, a couple of snails, four small "topwaters" (pond-bred descendants of local minnows) and two pond-bred small feeder goldfish. The goldfish are about 1", the minnows are about 3/4."

Fortunately, the horses are still happy to drink out of the trough! And they don't want to eat the water lettuce, so that will multiply and help shade my fish. However, horses are messy eaters and they're dropping a lot of grain bits in the water. The goldfish are hoovering the free food up off the bottom, and the minnows are scooting around the top eating whatever it is they eat.

I'm not really worried about oxygenation. The anacharis is actively bubbling off oxygen, the horses stir up the water a bit every time they drink, and I top off about 30-40 gallons a day with a hose.

Before and after I top off the tank, I use a large aquarium net to scoop up all the bits of hay and feed-gunk that I can get to.

Should I add more fish? Like I said, I've never worked with a system that has a lot of input before... I hardly ever feed my aquarium fish. My parents hardly ever feed their water garden fish. There's no way to prevent the horses from dropping food in. I'm worried that if I add a lot more goldfish that I'll have algae problems, though.

Also, is this a terrible experiment that's doomed to fail?

Thanks!

[Yankee Dog]

As you already know from your aquarium, the less fish the less maintenance. If you start adding more fish you are going to have to add a filter or end up with dead fish. Also, remember, the GF are going to grow.

Yankee Dog

[Squawkbert]

I'd leave well enough alone, and I'd add a little conditioner before topping off, unless you're on well water.

[Desertponder]

Wouldn't it have been easier to just buy one of those floating things that help keep algae out of your stock tanks??
Besides, tanks with plants and fish get quite a bit of crap built up in the bottoms. Horses need clean, fresh water to drink. I don't think I would want my horses drinking the water out of my water gardens on a daily basis. I don't even let my dogs do it.
We don't use a large stock tank for our horses. We use two smaller ones. They go through them pretty fast so they don't get algae build up so bad and they stay cleaner because we have to fill them every day.

[IceH2O]

I think you could do it without the fish, the food bits and bugs falling into the water should release enough ammonia to let the plants stay healthy. Plants prefer ammonia to nitrate from my understanding.

[cuticom]

Uuuh big warning here, I have an alpaca trough I converted to a pond, the trough was no longer in use, so I moved it up to the house. Anyways our cattle got loose one day and used the pond as a water trough, 3 of my fish got slurped up and the poor things were badly mauled, I had to put all three to sleep, I don't know if horses have the same drinking habits as cattle but if they do please dont put fish in there, I cant think of a worse death.