AboutJonathan Cauble Expertise I can answer all questions relating to outdoor water gardens. Anything from fish & plant health, water chemistry, and pond construction to equipment recommendations.
Experience I worked in a water garden specialty store for three years as assistant manager. I am also founder and president of Aquatech, LLC Aquarium Services of Virginia. I have personally troubleshooted over 100 ponds and countless aquariums.
Question I put copper sulfate in my pond to kill the algae two days ago
I now have about 60 dead fish. They are trying to get oxgen at the surface of the pond. Great big ones and babies are dying. they are catfish. If you could tell me what to to do to save them. Thank you.
Answer The first thing you need to do is perform a partial water change. Remove about 25% of the water from your pond and replace it with new water, making sure to add something to remove the chlorine. You may also want to buy a test kit for alkalinity. There are a few unfortunate things that may occur when using Copper sulfate (CuSO4) in a pond:
1) At low alkalinity/pH levels, Copper sulfate acts more strongly and creates even worse conditions. I personally wouldn’t use Copper sulfate in a pond at a lower alkalinity than 50ppm. It is also considered poisonous. Even worse, most pond-dwelling fish are more susceptible to death from CuSO4 poisoning than some other breeds of fish.
2) The algae absorbed the CuSO4 and once it died it released all of the Copper sulfate back into the water along with extra Carbon dioxide and decomposing organic matter. The algae also depletes oxygen as dies . Always make sure to remove algae as soon as it dies.
The solution to your problem would be to:
1) Perform the 25% water change I mentioned before (refill and dechlorinate).
2) Test you water’s alkalinity and use a pH buffer or baking soda to raise your alkalinity to about 140 ppm. Be careful doing this. A little bit goes a long way and it may also adjust the pH rapidly if you add too much at a time.
3) Also check any other parameters that you have the test for, maybe read an article online about checking water quality if you’re new to the subject.
4) If you decide to use CuSO4 again, try mixing it in a 1:1 ratio with lemon salt. It forms a more stable compound as well as allows it to dissolve better. You should be able to find lemon salt at a cooking store. Copper concentration should be at about .15 ppm. Make sure you don’t add too much; better to add too little than too much.
5) Continue regular 1o% water changes for best results.
You may want to consider an alternative form of algae treatment. You may consider:
1) An ultraviolet (UV) clarifier will knock “green water” or “pea soup” algae in a matter
of days. Barley products also do a decent job.
2) If you have a heavily planted pond (more than 40% of the water’s surface covered by plants) you will notice a huge difference in water clarity. This is because the plants shade the water from the sun and used nutrients that would otherwise fuel algae growth.
3) If you have stringy algae, you may want to consider a chemical approach. It is less expensive than a UV clarifier in the short term, but can prove to be rather costly over time.
4) One additional product out there is a sawdust-like powder that traps suspended solids. It is sold under many different names.
In order to save them, perform the water changes, observe and correct parameters (pH, alkalinity, ammonia, and nitrate). They might develop sores on their body from the stress they are incurring. To treat these, first diagnose them by comparing to a picture on the internet. There are really only about 5 likely things this could be. Treat with the proper medication.
In closing, every alga behaves differently. They all use basically the same nutrients, but in different ratios. Often times, by identifying the species of algae, you can determine what your pond has an excess of. Maintaining proper water quality, performing water changes, and including plants in your pond is actually the easiest and most long-term way to clear water. You may want to read an online article on algae because there are people with much more to say about that topic that I do.
All of the information here is intended for small water gardens (under 10,000 gallons) and not ponds measured in acres. It would cost too much money to do the things I listed and should be approached in a completely different manner.
