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What are winter fish kills and how can I prevent them? – Decorative Ponds & Water Gardens Q & A

Dyed Pond


Q: What are winter fish kills and how can I prevent them? – Alison in Illinois

Winter Fish Kills, They Don’t Float With Us!
You’ve waited all Winter long for the ice to melt over your water garden so you can run your waterfalls and enjoy your finned friends. Instead, you find your fish floating at the ponds surface, victims of a winter fish kill. What is this phenomenon and how can you prevent it?

Make Some Holes
When a layer of ice forms over the surface of you water garden, it essentially eliminates any transfer of air to or from your pond’s water. What this means to you is that, as debris decompose and your fish consume oxygen, byproducts are produced in the form of gasses that are toxic to your pond’s inhabitants. These gases are trapped under the ice and cannot escape; fresh air from outside the pond cannot reach the water either and so begins the process of the winter fish kill. Keeping a hole in the ice will allow the bad air in the pond to be replenished with good air. Some pond guys and gals use pond De-Icers to maintain an open hole, but many more rely on their aeration systems to do the job.

Pass The Bubbly
We’ve discussed in our past blogs the many benefits of aeration in your water garden. It circulates the water in your pond, infusing it with oxygen which is beneficial to your bacteria and fish. The constant bubbling produced by an aeration system will also keep a hole open in your water garden in the winter months, ensuring the release of those harmful gasses.

Being Supercool is SO Uncool
You have all heard concerns expressed in our past blogs in regards to “supercooling”. While this is a rare occurrence, there are a couple steps you can take to ensure you don’t overdo your winter aeration. When the cold weather comes, move your aeration plates to a shallower part of your pond. This will maintain a warmer layer of water for your fish to retreat to if the water does get a little too chilly. Furthermore, if you have a multiple plate system, you can run your water garden on just one plate for the winter. This will ensure that you have an open hole in your ice and should provide sufficient air supply to your fish as they require less oxygen during these times of decreased activity.

POND TALK: What type of aeration do you use in your pond? How have your fish fared over the past winters?

How do I control floating and bottom-growing algae in my lake? – Pond & Lake Q & A

No Algae Here!

Pond & Lake Q & A

Q: How do I control floating and bottom-growing algae in my lake? – Tom in New York

A: Whether it’s floating or submerged, algae can turn a lake into a green mess in no time. It’s unsightly, it’s sometimes stinky and in extreme cases, it can cause a fish kill. The good news is that algae can be controlled no matter what time of year. It starts with controlling the population and ends with a long-term management plan.

Before we dive in, it’s important to understand the difference between algae and weeds. The term “algae” refers to a wide range of single and multi-celled organisms that live in the water and metabolize carbon dioxide into oxygen via photosynthesis, just like plants. They differ from plants or weeds in that they don’t have true leaves, roots or stems.

In lakes and ponds, the most common varieties of algae include: Green floating algae that creates a “pea soup” appearance; Chara or Stonewort, which are a bottom-growing, seaweed-looking type that can be mistaken for weeds, and string or filamentous algae, which are actually long strings of algae connected together.

Sometimes, pond and lake owners may mistake duckweed for floating algae, but if you look very closely, you’ll find that it’s actually duckweed or watermeal. Check out this blog entry to learn more about controlling this invasive weed.

Population Check

If your pond is coated in pea soup or the bottom is carpeted in Chara or string algae, you can knock back the population with a chemical herbicide like Algae Defense® . It provides quick results and it’s formulated to get a pond under control – especially during the hot summer months. Do not use if your pond or lake is stocked with koi or goldfish. If your pond has trout, check your carbonate hardness with a water hardness test kit, like the Laguna Quick Dip Multi-Test Strips, and make sure the carbonate hardness is above 50 parts per million (ppm) before using Algae Defense®.

Long-Term Strategy

Algae Defense® by Pond Logic® will solve a crisis, but to keep your pond or lake looking clean and clear, you’ll need to be proactive and develop a plan to manage the algae. The most successful approach centers on cutting off the algae’s food supply – nutrients.

Nutrients can come from a wide variety of sources, like grass clippings, twigs, trees, fish waste, yard and farm fertilizers and runoff. As these nutrients break down, they produce ammonia, which triggers the nitrogen cycle. Nitrifying bacteria surround the ammonia, turning it into nitrites and then into nitrates (nutrients) – which then feed the algae.

So, how do you reduce the nutrients in your pond?
Try these tips:

  • Buffer before fertilizing: To prevent inadvertently fertilizing the algae, leave a buffer area around the pond. You can also try using organic or low-phosphorus fertilizers.
  • Aerate, aerate, aerate: Because that muck at the bottom of the pond feeds the algae, you should prevent the buildup with proper aeration.
  • Reduce the muck: Use natural bacteria like MuckAway™ by Pond Logic® to breakdown up to 5-inches of organic muck per year. You can also rake your pond using a Pond & Beach Rake to remove dead vegetation, leaves and other organics that will eventually decompose on the bottom.
  • Reduce sunlight: Like all photosynthetic organisms, algae requires sunlight to thrive. Adding pond dye can help provide shade. If possible, consider adding some non-invasive aquatic plants to your pond. The plants, which also consume nitrates, will also be a source of competition for food.
  • Add beneficial bacteria: You may also consider adding some additional beneficial bacteria, like PondClear™ by Pond Logic®, to your pond or lake. The bacteria gobble through nitrates, breaking down fish waste, leaves and other organics that accumulate in the pond, naturally improving the water clarity.

That green gunk can be controlled in your pond or lake. It just takes a little planning and some proactive management. When you see the results, it’ll be worth it!

POND TALK: When was your worst algae bloom and how did you control it?

Why Did My Fish Die Over the Winter? – Pond & Lake Q & A

Illustration of No Aeration Versus with Airmax Aeration

Pond & Lake Q & A

Q: I lost all of my fish after the winter. We love to catch fish in the pond and now we have to start over! What happened? And is there anything I can do to prevent this from happening again? – Alfred of Michigan

A: My first thought when I read this question was, “They don’t have an aeration system”. And after speaking with him, come to find out, he didn’t. This is usually always the case during a winter fish kill. Everything seems to be going just fine when all of a sudden one morning you wake up to discover a wave of fish floating on your pond’s surface. This is not a pretty sight, nor is it any fun to clean up. So what causes fish kill and what can you do to prevent it?

What Causes Fish Kill?
During the warmer months of the year a pond with no aeration will contain oxygen towards the surface of the pond. This is because there is an oxygen transfer from air to water at the pond’s surface. The bottom of the pond, however, will contain very little or no oxygen; Certainly not enough to support fish life. Also, the toxins associated with fish waste and other organic biodegradation tend to sink and stay at those lower depths of the pond, polluting the already oxygen-starved water. This unfortunately, condenses your fishes’ habitat area and forces them to live towards the surface of the pond.

There is also a difference in temperature from the bottom of the pond to the surface. The bottom of the pond will be colder than the pond’s surface. The reason for this is because the sun will heat up the surface of the water and since cold water is denser than warmer water, the cold water will fall to the bottom. This difference in temperatures can be quite dramatic at times. Have you ever jumped into a pond and felt the brisk cold water towards your feet? This is the thermocline border. This dramatic change in temperature can cause your fish to stress as they travel from a warm temperature to a cold temperature and back to warm. This stress can lower their immune systems.

During the colder months of the year, the oxygen as well as the thermocline will actually flip. All of a sudden the colder water containing no oxygen will mix with the warmer water with oxygen. As this mixing occurs, the fish are left with few places to go for oxygen and they will eventually suffocate.

Another issue during the winter are toxic gasses. As bottom organics (grass clippings, leaves, trees, twigs, fish waste, etc.) decay, they will create toxic gasses. When ice covers the pond’s surface, these toxic gasses are trapped underneath the ice and will cause a fish kill.

Preventing Fish Kills
Using an Airmax® Aeration System is the single most important way to help prevent winter fish kills. The reasons are simple: With an Airmax® Aeration System, a compressor sits on shore and pumps air down to a diffuser on the pond’s bottom. This air forces the cold water containing no oxygen to the pond’s surface. This water, because it is denser, will fall back to the pond’s bottom. This cycle will repeat and create a convection or current within the water column. This will fill the whole water body with oxygen as well as maintain the same temperature level throughout the pond (see illustration on left).

Also, during the winter months, when ice has covered the surface of the pond. An Airmax® Aeration System will keep a small hole open in the ice to allow those toxic gases to escape.

The Bottom Line: Having aeration will help reduce the chances of fish kill. Also, remember that this is one of many benefits of having an aeration system (Refer to this blog post for the other benefits of aeration).

Prevent Fall Turnover & Fish Kills by Using Aeration – Pond & Lake Q & A

Picture of a Fish Kill due to Fall Turnover

Being Aware of Fall Turnover.

Instead of a Q & A for Ponds & Lakes today, I wanted to make everyone aware of what Fall Turnover is and the steps you can take to protect your fish. Around this time of the year we receive quite a few phone calls from customers waking up to find a pond full of dead fish. Hopefully, I can shed some light on this subject that can help you prevent an event like this from happening.

What is Turnover? With no aeration present, the pond’s water is stratified (aka has a thermocline). Meaning that the water at the top is warmer and full of oxygen while on the bottom the water is cooler, nutrient rich and contains no oxygen. This causes the fish to habitate towards the surface of the pond. As the seasons change from the hot summer to the cold winter, the pond goes through a process known as “turnover”. This is when the cooler,
un-oxygenated water at the bottom of the pond, mixes with the warmer oxygenated water at the pond’s surface. Since the rising cooler water contains no oxygen, the fish lose the ability to breathe in a sufficient supply of oxygen. Shortly after, the fish begin to die.

Aeration to the Rescue! You’ve probably heard me talk about aeration in many Q & A’s over the past couple months and are probably sick of hearing about it. But it really is that important and really is a solution to a majority of a pond’s problems.

By properly aerating your pond, the oxygen will be saturated throughout the pond, thus eliminating the thermocline and eliminating the chance for future fish kills caused by “turnover”.

You can also under-aerate a pond as well. Please read the following Q & A for more information.

My Koi & Goldfish Were Gasping for Air After I Treated for Algae. What Went Wrong? – Water Garden Q & A

Picture of String Algae of a Water Garden.

Q: My water garden looked like pea soup so I treated it with AlgaeFix. The product worked great although it took its toll on my fish. My koi and goldfish began gasping at the surface. I immediately did a water change and only lost one small goldfish. I have used AlgaeFix for years and never had this problem. What went wrong? – Lisa of Georgia

A: Oxygen. Oxygen. Oxygen. You must be careful when treating for algae, especially pea green water or planktonic algae. AlgaeFix® along with most algaecides on the market work very quickly. When the algae die, they begin to decompose immediately, robbing oxygen from your fish.

How to reduce your chance of fish loss:

#1 – Proper Aeration:Make sure you have an abundance of aeration before you treat for algae. Waterfalls, spitters and fountains all provide aeration. Although, the best source of aeration is generally an aeration system.

#2 – If treating for string algae, remove as much by hand as possible before any treatments. In the case of Lisa’s pea green water, I would have recommend that she do a 10-20% water change approximately 24 hours before her application.

#3 – Get to the root of your problems: Generally ,excessive algae blooms are caused by one or more realistically, a combination of the following: poor filtration, TOO MANY FISH or not enough aquatic plants.

#4 – Use natural products to provide clear water: Although chemicals, when used properly, are a helpful tool they should not be your only solution. For a healthy eco-system and more consistent clear water, turn to a natural remedy such as the DefensePAC® and/ or Barley Straw Extract.

Be Aware of Oxygen Levels When Treating for an Abundance of Algae – Pond & Lake Q & A

Picture of Filamentous Algae in a Pond

Q: My pond was almost completely covered in algae earlier this month. With the advice of a local store, I treated my pond with an algaecide. Needless to say I suffered a terrible loss! What killed all of my fish? – Marie of Florida

A: More then likely your fish loss was due to oxygen depletion. It is very rare that an EPA registered “Aquatic Approved” chemical will cause a fish kill.

What causes oxygen depletion?
After a chemical application, algae and aquatic vegetation start to die and begin to decompose. The decomposition process requires great amounts of oxygen and can sometimes, like in Marie’s case, be harmful to fish. The chance of oxygen depletion is much greater when a pond is not maintained on a regular basis or when water temperatures are at their warmest such as the dog days of Summer. The warmer the water, the less oxygen it can retain.

How to treat your pond and keep your fish safe:
We recommend that you treat your pond in sections. The generally rule of the thumb is to split your treatment in to 3 parts or thirds. Treat 1/3 of your pond starting from shoreline working your way towards the middle. Allowing 5-7 days between treatments will greatly reduce, if not completely eliminate the chance of fish kill.

NOTE: Always follow the label rates on the container!

Reduce Oxygen Demand with an Airmax® Aeration System Airmax® Aeration adds oxygen to your pond reducing fish kills, while improving the overall health of your pond and fish.

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