Hi Pond Keepers!
I’ve been asked to write this quick blog on a controversial topic of using blue dye in your pond to stop algae and blanket weed. The reason I have been asked to write this blog is because for the last ten years I have owned and managed East Yorkshire Fish Farm, with 15 years before that a fish farm hand working my way up the hard way so in all that time I have come across many strange, bizarre and wonderful things that have happened around our own ponds; which over 25 years have stretched across 3 ten plus acre sites a canal we ran back in the 90s and many, many times we have been an emergency call out service for our long-time customers.
To the topic at hand, blue dye. This current year 2025 has had an amazingly hot spring and so much sunlight has caused many more ponds then usual to turn green. It seems every day I am getting two or three people ring me asking if they should add some sort or treatment to their pond this of cause is way up from only one or two people all spring in past years, I guess that’s why the koi world has exploded with talk around blue dye. So, what does it do and how does it work, well in basic layman terms, it stops sunlight getting into your water, creates a barrier between sunlight and any type of photosynthesis.
Think of sun burn, a little sun doesn’t burn or hurt your skin but a lot will, so you put sun cream on to stop anymore sun getting on your skin; too much sun in a pond, it goes green so you put blue dye to stop anymore going in, green water stops, well actually it dies off people think it just stops but it doesn’t it dies because it has no food, no sunlight no photosynthesise, so great no green water or weed right? Well, think what lives on that wonderful Phytoplankton [algae] we have just killed off?
Answer Daphnia. Well daphnia is the main thing I will talk about but so many insect’s koi eat live of phytoplankton all which carp prefer to any pellet preserved food, but back to daphnia, the number one best food of any omnivore fish. Koi carp, mirror carp, common carp of cause are all omnivore meaning they will eat just about everything. I cannot emphasise enough when I say the number one food for carp is daphnia, its full of protein, alive and fresh as can be, so small that it’s like perfectly designed for a carp’s unique digestive system. Or maybe the carp evolved perfectly to eat it. You see carp have no stomach at all. Inside a carp it’s all intestines. One of the reasons they seem to be always hungry, the food is always passing through like a conveyor belt. A lot of problems arise when something big or too heavy jams the belt causing food behind to block up more and more, daphnia been so small absorbs in the intestines so quick blockage is never even a thought. For me as a fish farmer my main goal of cause it to run a successful business. For me to do that the fish have to grow, that is where my profit is. Fish need room and food to do just that grow. Again, not only is daphnia a good food for them, if it takes off in a pond, we farmers lime and empty a pond to make sure of it. The result is clouds, masses of dense live food for carp to hoover up live baleen whale do in the ocean. [If your wonder what I mean just watch blue planet. I reckon every fish guy should anyway.] This great pretty much free food grows our fish quicker and cheaper than anything else. Unfortunately, it doesn’t last forever. April to June, three months of good cheap food. Free food from the sun. without that it would be just death to my business. I can’t throw that away just because my ponds didn’t look amazingly clear for a couple of weeks or blanket weed started to get out of control.
Now I do understand ponds do get stupidly bad with weeds in spring. Bad enough, panic can set in, but I have always found it happens for me at the beginning of the growing season when a pond is well under stocked and in my shallower ponds where the sunlight manages to get to the bottom. I say under stocked, because like I have said already, my business is to grow carp and carp need room to grow, so in April time I will, for example, put 400lb of carp in one of my acre ponds, loads of room and clouds of sun grown daphnia , by June, natural food will be gone the fish all doubled in size already so we will start supplementing the food with the best pellets. Again, keep in mind the best pellets aren’t anywhere near as good as naturals. we push the fish to grow more and up to the boundary of what biomass the pond will hold according to oxygen levels, not of course from what natural food the pond would normally hold, which in the wild is what normally holds fish back. This then tends to drive back all weed as the carp are turning the pond to mud looking for any scrap of left-over natural food. The mud then actually acts like blue dye, in that it stops sunlight getting into the pond, which is great because October generally means time to empty the pond, take every last fish out, lime the bottom to kill any organic waste to start the circle of free food all over again.
I guess what I’m saying is if you manage your stocking levels right weeds should never become a problem because your fish will keep them back for you. In fact, again they will become an asset to your pond proving warmth, food, protection and best of all add natural water filtration.
To sum up, I have tried my best to explain in easy and simple terms to anyone who’s new to fish keeping why on a fish farm where growing fish year on year is the business why blue dye just isn’t used. It’s not used because simply as farmers we do not.
“Take away the sunlight to help the pond life’.
The sunlight, the one thing that without they would be no life on earth, let’s take that away to help pond life, just let that sink in a minute, if you take nothing else from this blog take that away please. The sun, what every teacher as a kid told you, you need to grow anything, you’re wanting to take that away from your beautiful pond really?
Ok so I do understand that in some instances it could be used and know it has for a desired effect. Like a big lake that isn’t fishing very well, and the owners don’t have the funds to buy stock. If u kill the food source of the all the fish, chances are they will have to resort to the fisherman hook. The fish probably will be skinny and die off in winter due to no body weight but that’s a later problem, I know this sounds idiotic, but I have seen it all too often a lot of the time not surprisingly they buy fish the next spring of the guy who give them the advice to starve their pond.
Also, it could be used, [and I believe it is actually what it was intended for], is to stop blanket weed blocking up pumps and algae stains starting on big, beautiful fountains the type that live in town squares or for example in the king’s gardens.
I guess also if your pond was full of algae eaters like Grass Carp, Roach, Rudd, Sticklebacks, that you didn’t want but the pond was way too big and old to empty you could use it to take away the food source to starve them out.
Anyway, I hope this gives you fish guys out there something to talk and think about when it comes to ways to look after your fish and best little tidbit of advice for any people with a 5000-gallon pond of smaller suffering with weed or algae just put a cover over the top, just something to stop the sunlight, just like blue dye.
