Also, your filtration system will certainly help a great deal once that’s going. Same thing with desired plants. Often in the spring, these aspects of pond management aren’t in fill swing yet, while the fish may already be increasing nutrient loads.

As the desired plants come along and get into full bloom, and your filtration is up and running full steam, those will surely help with the balance.

Keep in mind, these beneficial things, along with other steps still may not overcome an issue of overstocked fish for the pond size. At some point, there’s no way around the fact that a pond of 4500 gallons will only hold so many fish safely…so that’s always a key thing to keep an eye on.

Your pond is large enough to serve as a good home for a lot of fish. Overstock is likely not a problem here. It’s hard to say why you have algae other than to say whatever nutrients that are supporting it’s growth simply aren’t being removed or balanced out.

Fish die off is always a concern, and it’s not a bad idea to check on oxygen levels and ammonia levels just to see where these are.

With algae though, I would make sure the filter system you have is adequate for the job at hand. Something easier to work with is supplementation with some beneficial bacteria at the start of every season. And particularly in the summer, you should try to add some helpful plants to the pond. Floaters that can help shade the pond and consume some of the nutrients that algae would feed on, might help.

Koi can sometimes get to eating at these, but it’s worth a try to see if you can bring about a balance to the pond. Once you’re able to do this, algae will likely reduce or go away completely on it’s own.

Just a few ideas to pursue as we move into spring.

Much will depend on how large your fish are in inches. 12 Koi isn’t necessarily a lot but again, how big have they gotten, and how much bigger might they get. That would be the important question in terms of whether your pond can provide a comfortable home for them.

If you have an algae issue, again, fish can have an effect. They may not be the only thing but they need to be considered. Work as best you can to keep a balance in the pond using plants (if possible), beneficial bacteria, and good filtration. That’s the ideal way to keep algae in check.

And thank you Mark…you’re correct, growth must be taken into account with fish. Just because you may have the same amount as last year doesn’t mean their influence can’t increase through growing.

Right you are on the amount of fish contributing to algae problems. One thing pond owners forget to consider is also the future growth of the fish in their water fish ratio.
Ponds should only hold half the allowed fish lenth/water ratio to allow for the future fish growth. Koi can often grow 1″ to 2″ each year in most regions and more in the warmer regions.

I would at least start thinking about how you want to manage this before things warm up where you are. It will help keep the fish that you do have healthier and happier.

Usually with larger ponds environmental factors play a great role than the fish do. This is not to say that a fish population couldn’t get too dense in a pond like yours but obviously there is a lot more room to play with.

If you have an odor coming off the pond, that’s usually indicative of a build up of decomposing organic matter at the bottom of the pond. Most often this is leaf debris or other matter that’s now turned rotten. I would suggest this is the root of your algae problem.

Aeration is probably helping as did the spheres. So much depends on how much build up is there. If it’s a lot, it may take time for this to lessen with periodic use of beneficial bacteria and aeration.

One thing you wouldn’t want to do of course is to kill existing algae off with a chemical. Then it will just sink to the bottom and add to the decay.