Is There A Conflict In Your Pond?

You’ve probably heard the saying, “oil and water don’t mix”, and that’s certainly true. A lot of people however don’t stop and think before they apply certain things to their pond in an effort to control algae. I’m not being critical here, it’s simply a matter of having the attitude that you want the stuff g.o.n.e., and no one can blame you for that.

The problem is more headaches can come up when you start trying to use products that really don’t go well together. There likely won’t be any explosions or anything dramatic, it’s just that you may not get the results you want with the algae.

So let’s talk about a few of the more common things that don’t quite jive when you’ve put them together in your pond.

UV Light And Beneficial Bacteria

UV or ultraviolet light is an effective tool to use against green algae problems in a pond. The single cell algae can create a pretty ugly look in the water, but UV light can kill or damage a lot of these little critters, along with other pathogens that float along in the water as it passes through the device. The problem is, there’s no way to tell it to leave the good bugs alone and kill only the bad ones. So good bacteria can be affected by UV too.

There’s a sensible way around this problem though, because if you have a biofilter working in conjunction with the UV, you’ll want to use bacteria to prime the filter from time to time. So here’s a good rule of thumb. When you’re adding bacteria into the pond system, be sure to turn the UV light off for 24 to 48 hours and allow the fresh bacteria to circulate throughout the system and into the biofilter more specifically. After it’s well established there, and in parts of the pond body too, then UV can be turned on and you should be good to go. Any free floating bacteria will still be affected of course but mainly you want it colonized in the filter and pond body where it will do the most good.

Copper Algaecides And Beneficial Bacteria

Now you may be thinking, these good bacteria aren’t very hardy critters if they can’t take a little light now and then. In truth though they are tough little things, but they are living afterall , and therefore, can be damaged by certain applications. So like UV, the same could be said when you use copper, or specifically, a copper algaecide to kill any algae directly. When you do this, you also kill good bacteria.

Before I get too far along here, let me stress that I don’t think any small pond owners should use much copper in a small pond at all. Copper Ionizers are used more commonly now and when they can be used safely that’s fine. Ponds without fish should have no problem with copper usage, but with fish, there is a risk of loss if copper levels get too high. Then again, if you have copper floating around in a pond, it will usually damage bacteria anywhere it’s present, meaning that the colony in a biofilter isn’t really that safe either.

So I see copper for a small fish pond as a no-no for the most part.

For large ponds there may, at times, be a use for copper algaecides but they are not the first line of defense against algae. I try other things first of course, and if one is required to clear up a pond, in a perfect world, you would likely want to follow up with some good bacteria supplementation a few weeks after a chemical application.

One of the biggest problems I see in large, old, ponds that have been treated with things like copper sulphate or Cutrine is a large degree of muck, sludge, and dead algae at the bottom. Common sense will tell you that this decaying stuff will only lead to more unwanted growth at the surface, yet the only way to reduce this build up is to either dredge the pond out, or use good bacteria to reduce the build up of organic debris. When you use a copper algaecide, it will bring this natural cleaning process to a quick halt.

Koi Fish And Desirable Plants (sometimes)

Quite often you’ll hear me suggest people use some good bacteria along with floating plants to help provide shade on a small pond. Doing these two things will often help with algae problems, and any number of other things, and it’s very wholistic. I mean who would have a problem with a few good lilies floating around?

Well in truth, some Koi (not all) will eat just about anything they can get their lips on, and desirable plants are not an exception. So rather than go overboard with plants to start with, it might be a good idea to test a few out with your current fish stock to see if they’ll tolerate a bit of foliage amongst them.

Good plants are such a powerful tool to use in keeping a small pond cleaner that they are worth the effort, but don’t be shocked if now and again you find a Koi munching on one of them. It’s not the end of the world, but down the road, you may need to look for other ways to shade the pond a bit.

Any Algaecide, Heavy Algae Growth, And Fish

Finally, this is a precaution we talk about a lot, but it can never be stated enough I think. If it saves one fish it’s probably worth the time to write this. No matter what type of algaecide you use, and this goes for the copper based one’s like Copper Sulphate, Cutrine, or even aquatic herbicides for large ponds, and things like Algae Off, Green Clean, Algae Fix and others for small ponds, the fact of the matter is, that if you kill a lot of algae or plant growth off at one time in a pond, you will pull oxygen from the water.

This doesn’t make some of these products necessarily bad, as it’s in the actual application where the trouble lies. Low oxygen is not good for fish.

Most of these chemicals, unlike a bacteria for instance, will work very quickly so within a few hours to a few days, the plant growth in a pond will die off pretty fast. The more die off that takes place, and the faster it happens, the more rapid the decline in DO or dissolved oxygen.

So on hot days, where pond water can’t hold as much DO anyway, it’s not a good idea to go on a plant killing spree in your pond. You’ll have some fish floating around soon enough.

Now, aeration will protect against this somewhat, but a better management plan would be more prudent. In other words, if plant growth is heavy, don’t try to knock it all out at once. Take your time, work in sections or segments, and gradually reduce the plants off, while you have good aeration running as well.

For small ponds, if you can remove some of the algae manually that’s probably best, then you can kill that which you can’t remove or get at, and probably be OK. Just remember, the smaller the pond, the more sensitive it will be to any changes in the water and to chemicals that may be used, so always err on the safe side in terms of dosage, and application.

Many Things Do Work Together Well

There are probably some other conflicts that could come up in a pond but for the most part, these are the one’s we see the most. Fortunately many things, like aeration, pond dye, barley straw, desirable plants, and manual removal of algae just don’t conflict with much of anything, other than maybe a bad back:(

Still knowing what will and won’t work together will help to keep your costs down, and your management practices sensible, and more effective, and that’s always a good thing.

2 Responses to Is There A Conflict In Your Pond?

  1. Nigel Pollitt July 11, 2017 at 3:19 am #

    Hi there, this is all very interesting what you’ve written. I have a question. I had a problem with duckweed (lemna) in my very bio-rich, fish-free pond (frogs, snails, huge number of crustaceans). After years of scooping it out, I eventually tried a bio-solution — a pond bacteria that sequesters phosphate and nitrate to kill off the duckweed.

    It worked perfectly, once the water temperature rose above 10C, as advertised. But, as warned on the pack, it harmed all the other plants too, in fact they all died — everything from elodea to grasses and water lilies.

    A year later, the anti-duckweed bacteria are still active and the only thing growing reliably in the pond are various marsh grasses. Everything else struggles. I am concerned that this is a very virulent bacteria and that I will have to start again completely from scratch. I have tried adding compost to enrich the pond, and this can give me a brief algal bloom, but for the rest, the water is very clear and plants are struggling.

    Is there anything that will kill pond bacteria, but not kill microorganisms?

    Thanks, Nigel, London, UK

  2. Mark July 13, 2017 at 9:34 am #

    Hi Nigel,

    Problem is that bacteria are microorganisms, so if you try to kill off some of it, you’re probably affect most all of it.

    Your experience is interesting to me because normally we don’t see harming of desirables so much…these rooted plants tend to be a bit more hardy and actually can be helpful with nutrient reduction, along with the good bacteria, and both work against algae blooms. It would not be fair to say that it is a cooperative venture but one of balance. If you felt you needed to start fresh you have a few options. Normally turning off any biofilters or stopping circulation, the bacteria in the filter will begin dying off within a few hours. Draining the pond would effectively do the same thing. You could try a shot of copper in there as that kills of most bacteria, both good and bad, but I would refrain from doing that with fish in there, as I don’t like using copper based algaecides in smaller fish ponds. I hope at some point you can find a nice balance with things where algae is limited but your desirables can grow well and be sustained.

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