If you have lots of plants in your pond there should not be a problem with green water, after the plants establish themselves. Don't add fertilizer at first, let the plants do their own thing.

You maybe wise to add a few minnows to help keep the mosquito larvae down, or use Mosquito Dunks. You can buy them at a garden store or Home Depot/Lowes.
"Horton"

I have found that floating plants like water hyacinth and water lettuce help a lot with algae and also in keeping the water clear.

I have wondered about mosquito dunks. Are they safe in ponds with fish? Though I haven't seen any mosquito larva, it seems like even with the fish, we have had a lot more mosquitoes in our yard since we've had the pond.

You could add a UV light and that would take care of the green water. My pond is in full sun and don't have a problem as long as the UV is on... turn it off and that is another story. BUT... If you want to keep fish my biggest concern would be that in that small of pond, things would really heat up quickly. Partial shade might be better.

As evesta notes a UV light can be quite effective. My spouse has 450 gallon in full sun and one UV light is effective most of the summer, she adds a second when the sun and air temperatures are high.

Is your pond going to be above ground or below ground? Either way, if you have 60% of the surface covered with plants, you shouldn't have any green water. While waiting for plants to fill out, you can shade the pond with an umbrella or shade cloth. Unfortunately, water hyacinth are illegal in Texas or I would recommend them too.

If your pond is below ground, you might be surprised that fish can survive over the winter. I'm in 8a and our first pond was a little peanut shaped pond and that first winter we had a hard freeze with ice so thick over the pond that we could stand on it. And still, the goldfish lived, we could see them through the ice moving around. The lily I had in it was toast though.

The next year I put the same pond on the south side of a building and everything in it did fine.

The mosquito dunks are absolutely safe for the fish. The only thing it works on is mosquito larva. It is safe for children. I have even seen a few of my fishies pushing the dunks around when they are bored. Sandy

marti8a why are water hyacinths illegal in Texas? Last summer I bought a house in Conn. with a small water fall/ water garden. I won't have fish. Just plants. I don't want to have more mosquitos than normal so I'll be looking into these dunks you're talking about.

Last summer there were water hyacinths and my water looked fine. It wasn't discolored at all. I threw away all the plants because I was told they wouldn't make it threw the winter. I guess I'll be buying plants every sprint. Does anyone know of plants that could last thru a New England winter? thanks.

buddyrose, like many invasive species, when they get into natural waterways, they can clog them and choke out native species which are food and habitat for native fish and other native creatures. Once their food source and habitat is gone, the critter dies, creating either a break in the food cycle or an opening for a non-native and probably undesirable species to move in.

Every state has their own list of prohibited species. Here is the one for Texas. Last I heard, the fine for being caught with hyacinth was $200. As much as I like hyacinth, it's not worth it to me, both the fine and the damage it would cause in our native lakes and streams.

Here is a link that might be useful: Texas Prohibited Species List

wow. good to know they're that invasive. they're not illegal in CT so I'll buy just a couple for my little water pond. They should fill it by themselves I guess once they spread.

You're probably cold enough that they can't survive a winter. Even here in north Texas where we get a few freezes, they will overwinter in protected coves.