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Understanding String Algae

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  • Except that - the string algae in the quarantine tank has appeared only on a VERY FEW occasions over the years - and it shows no sign, yet, of being there this year. I'll keep you updated.


    • Zinc Oxide

      Well, it is that time of year again. Postings about string algae (blanket weed) are popping up around the internet. All of the usual moans, groans, recommendations and comments are being repeated. One commenter on a popular U.S. forum has recommended use of zinc oxide as an effective, inexpensive and long-lasting remedy widely used in Europe. I do not know how widely used zinc oxide may be. I do, however, have great misgivings about the use of metals in koi ponds. My thinking parallels those of a regular poster on UK boards who goes by the handle Manky Sanke. His thoughts about using zinc oxide, edited down for space, are pretty much summed up in the following:

      Re: Blanket weed / Zinc Oxide
      Postby Manky Sanke » Wed Mar 26, 2014 12:58 pm
      I'm afraid there isn't a simple answer to this question but I can give some background information for anyone who might be considering using zinc oxide as an algaecide.
      Back in 2009 I went on a bit of a mission to see if there was any truth in a popular rumour at that time that Cloverleaf Blanket Answer was full of zinc that would guarantee to kill koi. ***
      At that time I was assured that there was some zinc oxide but that the content was trace amounts only. Zinc is essential in the diets of fish (and us) and zinc or zinc oxide is often added as a food supplement in human, animal and fish foods. …. I [liken] the necessity of zinc in a diet to that of salt which is a subject that we all understand.
      We know that some salt is essential in our diets and that we would die without it but very high amounts of salt in a single dose is fatal or that excessive amounts over a long period is bad for long term health. The same can be said of zinc.

      A couple of years later I was asked to help a health expert identify a few problems and there were suggestions that the zinc oxide levels were no longer only trace amounts and that the actual amounts in that product varied. I have no direct evidence as to whether that might be true so I can't comment on Blanket Answer but, in general, what could have been happening is that higher amounts of zinc oxide were dissociating (breaking down) into zinc under certain water conditions. The amount of zinc oxide that dissociated into zinc wasn't predictable so some people may have found the product ideal, some may have found that it killed their koi. That much I know is possible because chemicals in water behave differently according to such parameters as pH and anything in the water that might help to bind them in any particular chemical form.

      Zinc oxide [itself] won't kill algae but it naturally partially dissociates in water into zinc which is an algaecide. The question is how much zinc oxide is necessary, under any particular set of water parameters, to dissociate into a zinc concentration that is high enough to kill algae but not become so high that it will have a long term effect on the koi.

      It isn't possible to give a simple answer to that question because of the wide variations of parameters so if anyone says "this much worked for me" that isn't proof that the amount they used will be safe under all other pond conditions.

      *** I'm not sure that I'll ever be happy to recommend any zinc compound as an algaecide. There are people who use copper as an algaecide and swear that it's harmless to koi because they've used it for months and haven't wiped out their pond (yet?). Copper and zinc have similar effects in that they are definitely toxic and their toxicity depends on calcium hardness (CaCO3) and carbonate hardness (CO3). Their toxicity also depends on what other heavy metals might be dissolved. Lower pH and lower levels of GH and KH also makes them more toxic. Since sub-lethal concentrations of copper can accumulate in fish tissues and become immunosuppressants it's possible that a koi might survive being exposed to a low level of copper for years or it might fall victim to the first disease that comes along. Therefore a low level of copper might wipe out a pond this week if the pH, GH and KH are low but it may not kill any koi if they are high. On the other hand, the same dose of copper where the pH, GH and KH are high may cause the death of a fish next year if a disease infects it due to a weakened immune system, or never if the fish is never exposed to a disease. Copper toxicity is that complicated.

      My concern is that zinc, which is another heavy metal, will have similar complications regarding toxicity. That's why I said that just because someone says "this dose worked for me" that isn't a guarantee that the same dose will be safe in a different pond. *** But before I used any such product [containing zinc oxide] I would want convincing answers to "what research had been done, with what ranges of water parameters and over how many years?"


      • My water lettuce, aka quiapo in Philippines, does its job with nitrates and phosphates.

        Sent from my XT1068 using Tapatalk


        • Sent from my XT1068 using Tapatalk


          • String Algae As a Food: Supplemental Information

            In the event anyone has continuing doubts about whether string algae is a natural food their koi consume, I recently came across an ambitious study of the feeding practices of 16 herbivorous species of African rift lake cichlids. Among the subjects studied was the favored foods. The finding relevant to this thread: “A filamentous green alga, Cladophora sp., dominated the farms of most cichlid species, but was not ingested often. Cladophora are known to be unpalatable due to their chemical defences and poor amino acid contents. Therefore, this alga seems to be utilised as a substratum harbouring epiphytic diatoms for grazers and is a less preferred food item for other herbivorous cichlids. “ See, Hiroki Hata, Akifumi S Tanabe, Satoshi Yamamoto, Hirokazu Toju, Masanori Kohda and Michio Hori, Diet Disparity Among Sympatric Herbivorous Cichlids in the Same Ecomorphs in Lake Tanganyika: Amplicon Pyrosequences on Algal Farms and Stomach Contents, BMC Biology 2014, 12:90.

            Thus, even when focusing on herbivorous fish that have evolved in the company of Cladaphora algae, it is found that it is not intentionally consumed. There were, however, three species whose stomach contents included a measurably significant amount of Cladophora. Two of these were browsers in their feeding behavior and one was a ‘scraper’. No attempt was made to determine why these three species’ stomach contents differed. It may be reasonable to assume the ‘scraper’ consumed some Cladophora simply because it’s feeding behavior took in all algae on the rock being scraped, although other ‘scraper’ type feeders appear to have avoided Cladophora. With the browsing type feeders, incidental consumption could be the explanation. Given that Cladophora species dominated in all the feeding territories, I find it telling that none of the 16 herbivore species had evolved to take advantage of the most available algae. Cichlids are not carp, obviously, but when true herbivores avoid the most plentiful algae in their ecosystem, it is worth noting. String algae is such an amazing product of evolution.


            • Very good thread MikeM. Thank you for educating us.


              • I have not been by this forum in a very long time, but a fellow ponder pointed me to the link for this thread. I am glad that I dropped in. Mike, you have compiled a very useful resource of "current thinking" on the subject of string algae, to the benefit of many others. Thanks for going to the trouble of posting all of this information.

                BTW, I was also quite intrigued by Dr. Adey's recommendation/research of ATS, so much so that I actually did build one as part of my own koi pond filter system. Long-story short: the pond grew green water very well, but significant *turf* algae (Adey's term for it) never cultivated upon my scrubber surfaces. Mine was only lit by the sun -- no artificial lighting -- so that may have played a significant role in my lack of success with the concept.

                Thanks again for sharing the information of this thread.



                • Good to hear from you, Paul.

                  Sunlight should have been intense enough, but turf scrubbers have proved impractical/unreliable for the bulk of folks who have attempted them.


                  • ADDENDUM: Using Bentonite-Type Clay

                    Years ago, I posted above that I had not observed any significant impact on string algae growth from using powdered clay as an additive. That is no longer true.

                    In the Spring of 2020, while forced to stay at home due to the Covid-19 lock-down restrictions, I finally got around to cleaning out the garage. (I was really bored!) In the course, I came across a huge container of 'koi clay' I had acquired in bulk at some point years ago. I do not recall getting it. There must have been a 'going out of business' sale or some such for me to acquire so much of the stuff. I decided I might as well use it. It was early April, about the time of year when the string algae in my pond usually begins to have a growth spurt. Following the usual weekly filter cleaning and water change, I placed approximately 6 cups of clay in a bucket, mixed well with water, and slowly added it to my 12,500 gallon (U.S. gallons) pond. This was a lot more clay than is generally recommended on packages of the stuff sold to koikeepers, but I was wanting to use it up. When the clay started settling in the bucket, I mixed in more water and continued slowly adding it. The goal was to have it completely muddy the water. I accomplished that much... to the point that the koi more than a foot or two below the surface were visible as only vague shapes. After a few hours, the clay cleared. During the course of the week, there was a substantial increase in the amount of algae glarf captured in the mechanical filter stages. I continued this practice through early June, the usual end of the annual seasonal algae bloom in my pond. Over the following weeks, there was less algae glarf than normal. There was no outbreak of string algae in 2020. Over the summer months, I continued using the clay, but at the reduced rate of 2-3 cups per week following the weekly 30-40% water change. When the cool season arrived in December, I ceased using the clay. I still had not used up all I had on hand.

                    This Spring, I started using the clay again. I followed the same practice I had in 2020.... Weekly applications of about 6 cups to 12,500 gallons, perhaps a bit less on occasion. Once again, there was initially a substantial increase in the amount of algae glarf captured in the filters, followed by a substantial reduction below normal. It is once again early June and again there has been no seasonal outbreak of string algae, at least nothing approaching what I had come to consider normal for my pond.

                    As I posted above concerning the use of clay to control algae, there are several possible factors involved that could explain what appears to be a negative impact on string algae. Bentonite-type clay is known to adsorb ammonia and, to some extent, phosphates. This occurs primarily when the clay is suspended in the water column. When the clay settles, there is greatly reduced surface area exposed for adherence of pollutants. However, the clay particulate settling on the strands of filamentous algae limit light exposure and may interfere with the algae retrieving nutrient from the water column. There are no sufficient studies to give an answer. There are only hints of possibilities to be found in the scientific literature.

                    All that said, for two years there has been no noticeable outbreak of string algae in my pond. This is a dramatic change. I cannot say it was due solely to the use of clay, but I cannot identify any other change in practice that might have contributed. What is different is the quantity used. At the rate of a half cup per thousand gallons weekly for 8-9 weeks, followed by a quarter-cup per thousand gallons weekly for 6 months, there was a lot of clay used!

                    I still have some left, perhaps enough for another 6 weeks or so. I will then have used up that bulk package that had been pushed to a back corner of the garage. Did it really control the string algae? Was there coincidental factors involved? I do not know. What I do know is that if the powdered clay available was not so expensive, I would definitely continue using it. The idea of paying $4-5 per pound, plus shipping, for 20 and 25 pound packages (double and triple that much for smaller packages) makes me feel like a sucker. It's dirt! But, I'll be thinking about it......


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