Super high Phosphates in fresh water tank


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Hello,

I have a small 10 gallon fresh water tank. I have had it for about 3 years. I just got a pond and pond testing kit, just for kicks, I decided to test the aquarium's water. All was normal, but the phosphates was off the charts, like a 10 (the very bottom of the color chart!). Yikes!

Here's the weird bit, the tank is crystal clear. No algae at all that is visible - perhaps some gunk in the gravel, but outside of that, the glass is clear, the water is clear. I have several fish in there, lots of plants. I tested it twice to be sure, I couldn't believe the results. I'm terrible about cleaning it, but the plants keep the harmful bits under control.

Anyone think I should catch the fish, empty the tank and clean it fully and start over again? Or leave good enough as is?

Thanks,
Priscilla
 
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JohnHuff

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How often do you change the water in the tank and what's the phosphate level of your tap water? And the other readings of your tank water?
 
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tank readings
PH - 7.5
Nitrites - 0
Ammonia - 0

haven't checked tap water yet.

maybe once a month or once every 6 weeks. fish are growing and some have been there for at least 2 years.
 
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There are a few people (very few) trying to figure out why algae doesn't grow sometimes. I've had the theory that in ponds string algae produces a chemical that kills suspended algae. The process is called allelopathy if you want to search. Recently some aquarists have been using algae scrubbers to get clear water using string (macro) algae. Most believe the macro algae starves the green water algae. It's a very old myth and also widely believed in ponds. As you've seen clear water isn't related to nutrient levels. Even water testing 0 can still support algae because they consume it as soon as it's produced. When water tests 0 it only means very low amounts currently present. Like water will test 0 ammonia but we know ammonia is being produced. And of course the obvious problem with the nutrient theory is why doesn't the string algae die too. Suspended green water algae is way better at consuming nutrients, they're first in line at the buffet table.

You can do an experiment Norm Meck created. If you can get some green water you fill a jar say 1/4 full of green water and then the rest with water from your clear tank. If the allelochemical is present the green algae will be killed and slowly sink to the bottom. Norm's theory was the chemical was produced by bacteria, but I think the source is macro algae. Any way it's a way to determine what may be going on in your tank.

Slowly, very slowly, the concept of allelopathy is being considered by aquarists. Ecology of the Planted Aquarium by Diana Walstad talks about other kinds of plants in aquariums producing chemicals that kill algae, even string algae. I don't have a link, but I ran into a web page of an aquarist who was experimenting to try and see if he could id which plants were responsible for producing the chemical, or if many plants were. He named some plants he suspected, maybe they match what you have?

It's really unfortunate that allelopathy has been so slow to be accepted by aquarists. Understanding the process could really improve their hobby. Someday someone will identify some species of plants and do some experiment that will show the process better. I think that will lead to some people looking closer at algae scrubbers. That could even lead someday to understanding algae in ponds better. It could be a solution to string algae someday.

It's a shame the overwhelming pushing of myths will greatly delay getting there. Clear water and string algae free would be sweet. Allelopathy isn't even a new or controversial concept. It's been well known for a really long time in terrestrial plants and marine algae. Just for some reason people want to cling to old wives tales.
 
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