Pond algae needs certain things to grow really well. It’s a plant after all, and if you ask any good gardner what they like to see come growing season, it’s a nice balance of sun, rain, and some really good, nutrient rich soil.
For a pond owner, that “soil” might be at the bottom of the pond, or when it comes to nutrients in general, they could even wash into the pond in various ways. However they get in there though, the focus needs to be on reducing or managing these nutrients to keep algae in check.
Whenever you hear of someone having success on algae blooms, without using some kind of killing tool like an algaecide, you can bet that what really happened is that somehow, some way, the nutrients were simply made unavailable for algae to use to grow well.
While there are a number of nutrients in pond water, the one that probably has the most influence on algae is called phosphorus. Some experts have noted that for every pound of phosphate in a pond, 500 pounds of algae can be produced! So that’s quite a stimulant.
Phosphorus is a key element in nature though and it really is a beneficial thing to life on earth. It’s just that too much, in the wrong place (like your pond) can be a problem.
Where Phosphates Come From
Phosphates can come from a lot of places but the most common sources are, well, quite common.
If you live in agricultural lands, then fertilizers containing phosphorus are used frequently. Runoff following rainy days, can go directly into the pond or via source water from incoming streams and spike the nutrient in a pond. Leaves, as they decay, can give off phosphorus, as does the waste material from waterfowl like geese and ducks.
If you feed your fish, many commercial fish formulas contain phosphorus (some of it is quite healthy for fish) but if a lot of the food goes uneaten, it would be added directly to the water.
Phosphorus Isn’t All Bad
It’s important to not give the impression that phosphorus or phosphates are all necessarily bad things. They aren’t. As mentioned before, the nutrient is critical to healthy life on earth. Plants benefit from it greatly, as does every living thing. Without it we’d be in a world of hurt.
But it’s critical to remember that algae and other aquatic weeds use it for rapid and expansive growth so if you’ve got an ongoing, hard to control, weed or algae problem, then phosphorus really should be analyzed. If the readings are fairly high then it makes sense to do something about it.
The funny thing is, it’s not really accurate to say that phosphates were reduced in a pond. They don’t go anywhere really. But the most effective way to reduce their effects, is to bind to them with something that makes them unavailable as a food source for algae.
Aluminum Sulphate Binds To Phosphorus
One of the most common binders that you’ll see marketed today is called Alum, or Aluminum Sulphate. It’s an excellent chemical phosphate binder. But one precaution related to Alum is that it’s very acidic and it can drop the pH of the pond water very quickly in some instances. It’s for this reason that I’d suggest avoiding the use of unbuffered Alum. Buffered formulas that include Alum along with Sodium Bicarbonate will help to offset some of the effects on pH.
Some specialized formulas use polymers along with lower doses of Alum and these have much better stability in terms of how they affect pH. Then there’s another, all natural, calcium based solution which is completely organic and won’t affect pH at all. Currently we prefer this formula over the others. It works more slowly but is an effective tool for taking the available phosphates away from the ravenous algae cells that love them so much!
And what about dosage rates. Well, from product to product you’ll find some variability here. Follow the suggested label directions and dosing of whatever you’re using. Remember though that these rates will vary a lot based on the amount of phosphorus in your pond water. Higher doses of any binder will be required for high levels of phosphate. In most cases you can add repeated doses as needed while checking phosphate levels as you go. The goal should be to keep them down around 10 to 30 ppm or less.