A Leading Cause Of Algae In Fish Ponds

As far as small fish ponds go, pond algae is a pretty common problem. In truth, you don’t necessarily need fish to have algae issues but there’s no question that our finned friends add another dimension into a water garden that may promote the growth of algae. I say “may” because you can’t correlate fish and algae blooms 100% of the time. Nevertheless, the two go together often enough to encourage us to look into the reasons why.

There’s good news here too because for the most part, as the pond owner, you can control most of these things in one way or another and that means you have a direct influence on these frustrating algae outbreaks.

How Many Fish Is Too Many?

This is what I call the “sardine can effect” and it comes from watching my father-in-law snack on sardines and crackers. Have you ever noticed how many fish are crammed into that tiny metal canister? It ain’t pretty.

Believe it or not, a similar, although less dramatic event can happen in a small pond. Every pond, no matter it’s size, will only be able to safely hold so many fish. There are limits to everything. The overall gallon volume and size of the pond will be the first limiting factor.

Here’s a general rule that we’ve noted many times. You should allow about 25 gallons of water for every inch of Koi, and about 10 gallons for every inch of Goldfish. So you want to take a bit of time and estimate the number of fish that you have in the pond, their average size in inches, and what type of fish they might be, then run some numbers. If you have 10 Koi that are on average, six inches in length, that’s a total of 60 inches of fish. If we take 60 times 25 (gallons), we come up with 1500. In other words, you’ll need a 1500 gallon pond or larger to hold the fish. If your pond is only 500 gallons, then a high fish loading could be part of the problem.

Fish create waste which, as it’s naturally processed, will end up feeding plant growth and it’s direct stimulant for algae. A good filtering system, and particularly a well fitted bio-filter, will help a lot with this stuff, but once again, they have limits too, and they are normally fitted to a pond’s gallon size.

As fish grow and multiply, it’s just not that uncommon to go along with no problems for a few years, and then all of sudden find algae growing well once a particular threshold is reached. At this point you have a couple of options. You could add more robust filtration, but the easiest thing is to reduce your fish load. Find a home for some of the fish and reduce the burden on the pond. I’ve written previously about what can happen if you don’t take this important step and you can read about that here.

Don’t Get Skimpy With The Filters

Speaking of pond filters, we really need to note them here because they have a direct effect on water quality. When you’re designing your pond or building one for the first time, it’s really smart to plan ahead. Of course a filter needs to be adequate for a pond’s gallon volume, that only makes sense, although you might be surprised at how many do-it-yourselfers cut corners on this to save a little bit of money.

If you never planned on having fish at all, you at the very least must get a filter system that’s equal to, or a bit more robust when compared to your pond’s volume. When you add fish into the mix, you’ll need to bump the filter’s capabilities up quite a bit. If you look on the sizing chart on our filter page, you’ll see that gallon volume is noted, but right next to this is a section for “pounds of fish” so these need to be part of the equation too.

It’s important therefore to not get to skimpy with the filter selection at the outset, unless of course you like extra challenges later on.

One of the natural tools that you could use, should you find that your filter system is a bit outmatched, is to add desirable plants into the pond. These are very useful at adding another form of filtration and nutrient absorption into the mix. It doesn’t so much matter what you choose. Just pick some plants you like and start building up their density in the pond. You’ll know when you get the amount right because algae will start disappearing. Using a bit of beneficial bacteria routinely can also help as it works with the plants to reduce nutrients.

Fish Food Plays A Part

I ran across an article recently that discussed a very interesting element to pond care, but before I get to that I want to lead into this section by simply suggesting that part of your pond’s water quality problems could be coming from uneaten fish food. It’s a common problem and one of the simplest things to adjust for the pond owner.

Fish food is nutrient dense, and it’s also organic, meaning that when it breaks down, it will provide nutritional support for algae growth, just as all organic substances can do. Ideally you don’t want any of this stuff accumulating at the bottom of the pond so if you’re feeding fish, make sure they pretty much eat everything you put in the water. Slow down on your feeding routine or reduce the number of times during the day that you feed them and pay attention to what’s happening. If you see food going uneaten, be sure to cut back a bit.

And finally, this may seem like an odd thing to say, but in a way it makes some sense. Be aware of your own appetite when you go out to feed your fish. You’ve probably heard of the advice that you shouldn’t go shopping at the grocery store on an empty stomach? For people that do this, they end up buying more than they planned on…sort of a binge buying spree you might say. Well interestingly, at least to me, research has shown that people tend to overfeed their fish when they themselves are hungry! The lesson here is to be sure to take care of yourself first, then go feed the fish.

The rule of thumb successfully used for many years is to let your pond fish eat all they can within a five-minute window (with a well paced level of food distribution, ie don’t just dump it in). If any food remains after the five minutes, the fish were over-fed.