Blanket Weed/String Algae

Discussion in 'Water Features' started by RockSet N' Grade, Mar 16, 2007.

  1. RockSet N' Grade

    RockSet N' Grade LawnSite Silver Member
    Messages: 2,454

    We have a 4,000 gallon pond with 5 koi. This is the second year for our pond.....we have plants covering about 35% of the surface. Have a waterfall with filter and pump system. Our problem is we are getting an overabundance of blanket weed and string algae and would like to minimize both, without harming the koi and other plant life in the pond.........any thoughts?
  2. Victor

    Victor LawnSite Bronze Member
    Messages: 1,430

    One tactic I've had great success with has been to do large water changes (at least 25% per week). This way you're not introducing unneeded chemicals into your pond. You're actually helping the fish, while you're controlling the unwanted algae in your pond. Wet Pets in Georgia put me on to this algae-controlling trick years ago. Chuck Jones (owner of Wet Pets) and his staff have to be some of the most knowledgeable people out there when it comes to koi ponds and their upkeep.

    I was skeptical about this tactic at first, but it has really worked well for me. The large water changes tend to starve the algae for nutrients. When you do large water changes like that, you're removing large quantities of nitrates (the plant food algae feeds on).

    Unfortunately, there's a lot of mendacious information about algae control out there. I've tried a lot of these ideas over the years and have found few of them to be effective.

    By the way, I hope you have a dedicated water meter for your pond. If you don't, doing water changes in a pond that size can be very expensive. On a pond your size, it's almost a requirement.

    Now you know I'm gonna want to see some picks of your pond. No hurry. Whenever it's convenient. Take care. :)
  3. RockSet N' Grade

    RockSet N' Grade LawnSite Silver Member
    Messages: 2,454

    Victor, the real owner of this pond (my better half) does the 25% water change on a regular basis. She vaccums the bottom of the pond when weather permits ( its just turning spring here).....but that blanket weed and algae keep going. She has even taken water samples to be analyzed and has her own testing kit to keep the water ph where it is suppose to be. Any more thoughts on this little rascal?
  4. Az Gardener

    Az Gardener LawnSite Gold Member
    Messages: 3,899

    I am having the same issue with string algae and we do a 20% water change out 2 time a week. The stuff is just stuck to the walls, I am going to get the vacuum on it next week but I am not optimistic. I think I will be wire brushing it.
  5. Victor

    Victor LawnSite Bronze Member
    Messages: 1,430

    The only thing I can recommend thaat you do, is to increase the % of water that you change out each week. You could try 50% water changes. The only concern I'd have would be the expense involved if you don't have a dedicated water meter for the pond.

    Do you have any pics of your pond that would show me your fitration and how its set up? If the increased water changes don't work, you might have to resort to chemical options.

    AZ... The algae that your talking about being on the walls of your pond is string alagae? The reason why I'm asking this question, is because there is a beneficial type of algae that normally grows on the wwalls of a pond. Its different than string (blanket) algae. It doesn't normally grow out into the pond thhe way string algae does. It normally just clings to the walls (acting as a great nitrate sponge).
  6. Az Gardener

    Az Gardener LawnSite Gold Member
    Messages: 3,899

    This stuff is growing straight out from the sides into the center of the pond. Right now it is 6"-8" long the water is clear due to a pool style filtration system and the twice weekly backwashing.
  7. Victor

    Victor LawnSite Bronze Member
    Messages: 1,430

    Sounds like its definitely string algae then. One option that would not only curb your string algae problem, but would also prevent problems with Herons would be to drape shade cloth over your pond this Spring. Spring is when problems from these two pests are most common.

    Shade cloth is something both of you should consider. You can buy it for around 75 cents per sq. ft. right now.
  8. Fishwhiz

    Fishwhiz LawnSite Member
    from Oregon
    Messages: 112

    In a pond you are not feeding, you might consider that introducing new water also introduces new nutrients that the algae take up and hold in your pond. The more you change the water, the more nutrition you add unless your water supply is nearly devoid of minerals. If your pond is small enough, it may be better to vaccum the algae since you always want to remove the greatest amount of nutrition.
  9. janealvarado83

    janealvarado83 LawnSite Member
    Messages: 1

    One way to minimize string algae is to create an unfavorable environment for your pond - that is, add more pond plants to keep away direct sunlight or reduce the number of fish to lessen the amount of waste (which blanket weed love). When I had this problem in my pond, I manually removed the bigger portions of the algae and then add beneficial bacteria. I used Aquascape's SAB. It pretty much did the trick. I don't have much algae problem anymore, though string algae do come back sometimes. Some people advise using UV lights. I still haven't tried it but I'm planning to. I hope it will be effective. The Pond Blog has a post on string algae that pretty much helped me out. Take a look:
  10. tadpole

    tadpole LawnSite Bronze Member
    Messages: 1,221

    The presence of excess algae does indeed indicate a high nutrient level in the pond water which is usually a combination of NitrAte and Phosphorus. String algae has a particular affinity for phosphorus. Phosphorus levels should be kept at <5 mg/l. Most organic debris (leaves, twigs, grass clippings, uneaten fish food) will increase phosphorus levels. Any phosphate binding product, used correctly, will control, if not eliminate, string or filamentous algae by reducing the phosphorus levels. UV clarifiers have no effect on either string algae or blanket weed. UV clarifiers only destroy those algae cells that pass directly past the UV lamp.

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