Forum home› Problem solving
This Forum will close on Wednesday 27 March, 2024. Please refer to the announcement on the Discussions page for further detail.

Green slime in fish pond...blanketweed? Dangerous to fish?

CulpabilityBrownCulpabilityBrown Posts: 63
in Problem solving

I recently noticed a load of green gluey slimy stuff growing in the centre of my large fish pond.  I noticed my large fish were right in amongst it, and seemed to struggle to make their way through it, as though it was sticking to them and preventing them from swimming freely.  When I dragged some out to the edge it was very stringy looking, I looked it up and I think it is blanketweed.

Is this stuff dangerous to the fish? Could they get trapped and die? What would people advise? Should I dredge it out to the edges and compost it, or just leave it alone (I've read that blanket weed usually dies off once the other plants grow in around it)?

«1

Posts

  • FairygirlFairygirl Posts: 55,117
    It isn't dangerous, just messy.   :)
    A stick [or similar] stuck in and wound into it will collect a good bit of it, and you can then leave it at the side of the pond for any wildlife to get back in easily. It can be composted once it's been left for a few days to do that.
    It's common when water starts to warm up. Plants which cover the surface are useful to help keep some shade, and therefore keep it at bay, as well as oxygenators which help use up the nutrients it feeds on. I use watercress for that, just chucked in, and it covers early in the season, and floats as well as rooting around.  
    It's a place where beautiful isn't enough of a word....



    I live in west central Scotland - not where that photo is...
  • CulpabilityBrownCulpabilityBrown Posts: 63

    My best guess is that it grew in after the water level rose recently (which submerged the plants that would usually shade the top area).

    Yes I've heard of the watercress tip, thanks for reminding me! Do you know if fish are okay with watercress?

  • FairygirlFairygirl Posts: 55,117
    I can't see it causing them any problems. 
    It's a place where beautiful isn't enough of a word....



    I live in west central Scotland - not where that photo is...
  • brackenbracken Posts: 91
    Barley straw helps to combat blanket weed.
  • CulpabilityBrownCulpabilityBrown Posts: 63
    I'll give them both a go if it gets really bad, thanks!
  • jonathanYkqOIwpcjonathanYkqOIwpc Posts: 1
    The use of a stick is by far the best way to remove it.  I was commissioned by Gardening Which? To test garden pond algae control products when I worked at the Centre for Ecology and Hydrology. Sticks gave 100% control at the end of the test.  A split bamboo cane  works really well.  Blanket weed is the best habitat for aquatic invertebrates that fish feed on.  It’s not toxic, but it can cause problems with fluctuations in dissolved oxygen.  It will produce lots of oxygen during the day, which might also explain why the fish are crowding around it, but it will consume lots of oxygen and produce carbon dioxide at night.  These fluctuations in dissolved oxygen are also accompanied by changing the pH of the water ( alkaline in the day and acid at night) that also causes stress to fish.  It’s best to remove it by winding around a stick, leaving the stick above the pond to allow the invertebrates to fall back in.  It will eventually disappear but it starts to grow in cooler temperatures than other plants, so often gets ahead of competing plants. The more plants with exposed roots in the water you have the better, so watercress is good, but may also need control later.  
  • CulpabilityBrownCulpabilityBrown Posts: 63

    Hmmm very interesting re pH etc, I've got a huge old bamboo stick somewhere, I'll give it a crack.

  • LynLyn Posts: 23,190
    I found twiddling it out of my then new pond,  very therapeutic  when I had some troubled times. 
    Once we get some sunshine and your other plants start to grow, I'm sure it will go away. 
    I only had it for the first year. 
    Gardening on the wild, windy west side of Dartmoor. 

  • FairygirlFairygirl Posts: 55,117
    I've never had much faith in the oft recommended barley straw solution for it. I've tried it i n a previous pond and it did nothing. Interestingly, I read an article recently that stated there was no real support for it working effectively, so it made me feel better.  :)
    I've never had a problem with watercress becoming a nuisance either. It's easy to pull out anyway. 
    If you have fish, they'll produce more waste, so you may need to work a bit harder with your blanket weed @CulpabilityBrown :)
    It's a place where beautiful isn't enough of a word....



    I live in west central Scotland - not where that photo is...
  • FireFire Posts: 19,096
    Sticks don't make it go away and are useless in microponds which can fill up with blankweed. It's hard to get rid of. Barley straw /extract doesn't seem to be helping either.
Sign In or Register to comment.