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How to Clean a Large Fish Pond With Algae and Pond Weeds

Here's the top 10 steps to take to clean your large fish pond of unwanted algae, pond weeds and sludge and muck build up. (If your pond or water garden is smaller than this please check out our backyard pond and water gardening cleaning tips.)

1.  Get a lake rake and remove as much fallen leaves and dead aquatic weeds that you can.  We have a variety of lake rakes and aquatic weed cutters to use.  Do yourself a favor and have a 'party' or BBQ with family and friends (if your pond is big) and they can give you a hand especially if they will be enjoying it with you.  It can be a heavy and daunting task but one where time goes by quickly with friends, food and drinks and with stories to tell for years to come.  (Hey!  Remember when....) 

2.  Put that sludge, muck and dead aquatic leaves in a big pile or if you can, spread out in a garden or somewhere and use some of our PlanktoniX beneficial bacteria on it.  PlanktoniX works GREAT at decomposing organic wastes in OR out of the pond!

3.  Put in a proper size aerator especially a diffused aerator that you can use year-round.  Aerators add necessary oxygen to your pond for it to be healthy and for your fish to survive.  We can help you select one.  They're super easy to install and can last you for many, many years.  Their benefits are substantial and they're very energy efficient and much more efficient than a fountain or waterfall that don't oxygenate to the bottom of the pond - which is what you want.

4.  If you have lots of green water algae I need for you to understand what causes it and why it's important you follow some very simple, yet super effective steps to get rid of it. 

Green water algae is caused by excess nutrients from fallen leaves, dead aquatic plants, fish wastes, sludge, muck, etc..  All of these organic wastes are providing food for your algae to grow!  So, go back to step #1 and remove as much fallen leaves and dead aquatic weeds as you can as this can save you a HUGE step and expense.  Also, do what you can to eliminate fallen leaves, etc. from getting in the pond in the first place.   We have a variety of pond nets and seine nets you can use to cover or seine the pond to do that.  You could also install a pond skimmer  (if you have a liner pond) that will siphon off the leaves and debris that blows into the pond and later sinks. 

5.  To treat the pond naturally, you need to add some PlanktoniX pond bacteria  (available in different sizes) which will start eating up the sludge, muck and other organic matter that is providing food for your green water algae (and unwanted weeds, too) to grow.  You can add several times the dosage and perhaps even a lot more than that to really have a powerful army of bacteria eating up that sludge.  (If you're interested in an accelerated decomposition of this organic matter, let us know so we can advise you how to do this.  We have helped save hundreds of thousands of dollars to many folks who thought the only option was to dredge their pond. )  Use the PlanktoniX faithfully all season long.  Don't skimp; don't forget.  PlanktoniX will be your #1 best friend to keeping your pond clean.  

6.  A lot of people want a 'quick fix' and want their green water cleaned NOW!  I'll tell you what you can use to do that but know that this is a temporary solution because more green algae will grow again because you haven't gotten at the root of the problem by eliminating all the sludge and muck in the pond that's feeding it and causing it to grow!  You'll actually be adding to the problem because your first 'treatment' of killing pond algae will cause the dead algae cells to collect on the bottom of the pond which gives more and more food for more algae to grow.  But, you want to know how to kill the algae now, and I'll tell you...

7.  You can use some Cutrine Liquid or Green Clean  (both available in granular or liquids) or a different algaecide but do know that some of these are restricted chemicals and cannot be used in every state.  You also cannot use these if your pond is not 100% contained on your property and has a small stream going to or from your pond.  In this case, your local DNR (Department of Natural Resources) has jurisdiction on what you can do, if anything to your pond because it would affect part of our public water system because water flows to or from your property from other properties.  

All of these algaecides work pretty much the same way.  They'll kill your algae and the dead algae cells will sink to the bottom causing more food for more algae to grow.  Copper sulphate creates almost a sterile bottom because the copper builds up in the sediments and the beneficial bacteria can't grow in it besides other helpful 'creatures'.  We don't recommend the use of copper sulphate nor do we sell it.  Cutrine Plus is a chelated copper and is more effective and safer to use because it doesn't 'release' the copper ions like copper sulphate does which harms the environment.

8.  You can use an aquatic sunblocker that will block a lot of the sun's rays from entering through the body of water.  Algae and pond weeds need sunlight and food to grow.  You starve out the algae from food by cleaning up the sludge and muck by using the PlanktoniX faithfully.  You starve out the algae and pond weeds from sunlight by using an aquatic sunblocker or 'pond dye' such as Aquashade or Black or Blue Vail For these aquatic sunblockers it's best to start EARLY in the season before the green water algae and pond weeds start to grow.

9.  Now, the pond weeds.  You need to have them properly identified.  We have a chart on how to determine what type of pond weeds you have.  If you're not sure, you may be able to take a sample into your local DNR or county extension office and they may be able to determine what pond weed you have.  Call beforehand to be sure if they provide this service. 

There's a variety of pond weeds; some are submerged or living totally below water like hydrilla and others may be floating like water lettuce or water hyacinths while some may be partially submerged that has roots that grow in the water and the rest of the plant grows out of the water like cattails do.  You need proper identification.  That's a must.  If not; you'll be wasting your hard-earned cash and putting chemicals in your pond for nothing. So, proper identification is crucial.  Then, you can go to our pond weed chart and see what chemical or 'aquatic herbicide' will work for those pond weeds.  Again - and just like for algaecides - you cannot use these chemicals if your pond isn't 100% contained on your property or if you have water that flows to it or from it.  You must contact your local DNR (Department of Natural Resources) on what you can do, if anything.  If you use something and get caught, it can be a huge fine for you besides polluting our public water system.  So, be warned and informed of this.

Most pond weeds do best by treatment early in the season, particularly if you're treating the whole body of water.  This 'nips it in the bud' and doesn't allow them to grow prolifically during the season and may kill them altogether - depending on the product. 

There is also something that's called, 'Sonar' which is a broad spectrum aquatic herbicide that works for a lot of pond weeds.  It's 'expensive' but can last for more than one season and often for 2 or 3 seasons. 

Always follow instructions for using pond weed killers.  When pond weeds and algae die they rob oxygen from the water and can rob your fish of oxygen they need to survive.  You can lose a lot of fish if you over treat the pond or don't follow instructions because of this.  A lot of times you can have that aerator I told you about turned on and that can definitely help A LOT.  Also, sometimes it's recommended by the manufacturer to treat 1/3 of the pond at a time and most of the reason is because of the dieing plants consuming oxygen and not enough oxygen is left in the water for your fish.  This may be more common with herbicides that act quickly whereas something like Sonar acts slowly but lasts for a much longer time.

Also, for cattails, it's best to treat them late in the season when the brown cattails have formed so the vim and vigor has left the plant and it's more easily treated and killed all the way to the roots. 

While we sell aquatic weed cutters I personally don't recommend them for weed eradication as cutting the plants down only encourages a stronger root system so more plants will grow and more robustly.  Use the right aquatic herbicide - aka pond weed killer - and at the right timing for best effects.  Some people have spent hundreds of thousands or millions of dollars dredging out large ponds and lakes.  This can be totally unnecessary with the right pond weed killers, instructions and timing of their use. 

10.  That's about it.  Clean the organic matter out as best as you can with a lake rake.  Get a proper size aerator and use it 24/7/365.  Use PlanktoniX all season long and use it faithfully.  Do what you can to eliminate as much organic matter or fertilizers from getting in the pond to begin with.   Use an aquatic sunblocker such as Aquashade or Black Vail, Blue Vail or Black/Blue Vail and start early in the season for best results to reduce or eliminate pond weed growth early in the season and use the right aquatic herbicide for the pond weeds you have to kill the weeds systemically.  Consider a broad spectrum pond weed killer than may last more than one season.  Remember to contact your local DNR as to what chemicals you can use, if any, if your pond and it's water flow is not 100% contained on your property.   The Department of Natural Resources has jurisdiction on what you can do and you can be issued a hefty fine for doing something you shouldn't besides it affecting the public water system for everyone.

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