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Green water than mass die off.

aarendse

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Hey all. I have had tropical freshwater tanks for over 10 years now and usually never had much issue, until now. I got a new 30 gallon tank from my sister who was done having a tank. I set it up, let it cycle, then moved my fish over. They all seemed happy and well. This was about 6 weeks ago now. In my tank were 4 male guppies, 4 neon tetras, 1 emerald green cory cat, 3 peppered cory cats, and 2 oto cats. Now 3 days ago my tank went green overnight. Pure green water. My fault really, I left the big window open and shining on it and didnt do the weekly water changes the past couple weeks like I should have. Figured normal algae bloom. So I put in my algae killing drops and did a small water change. Waited 2 days, like it says, and did that again. Almost immediately 2 of my guppies and 2 catfish started acting like they had bloat. So I did a massive water change (about 75%) because my main worry was the algae killing drops were harming my fish. I got up this morning to all 4 of those fish dead, my other guppy isnt doing well and 2 of my neons have lost their neon. I use testing strips for water testing and show zero nitrates and nitrites and 7.0 ph and both hardness are within range. I do not have an ammonia tester so I dont know those numbers. Could my algae killer have done in my fish that quick or do i need to look into something else? I weekly test my water but changes have gotten hard with theis covid stuff and me working lots in a hospital. Any suggestions on what else to look into or buy to test my water or anything is helpful. I hate seeing my fish suffer.
 

utahfish

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Not sure how algae killing drops work but i cant imagine its good for fish. Next time skip the killing drops and do a large water change.
 

Munroco

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I think lghting is likely to be the problem. You don't mention if you have plants or not, but it seems you will have to find a balance that suits your tank. Try differing lengths of time the light is on (obviously you will need to wait a few days each time to see if it's making a difference).
 

Retired Viking

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The tetras lost their color due to extreme stress. What type of algae killing drops did you use? Also algae like any "plant" releases co2 at night and absorbs oxygen. This could also be the problem with so much in the water.
 

Retired Viking

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When ponds around here get over run with algae due to algae blooms there is a mass die off of fish due to a lack of oxygen and some algae releases a poison as it dies
 

seangee

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For future reference algaecide is poisonous (to fish as well as algae). Algae is caused by an imbalance in light and nutrients and it is always best to address the source.

When a lot of algae is killed it affects the amount of oxygen available and can also cause an ammonia spike as it means the tank is suddenly full of dead and decaying organic matter. Best to do another water change and deal with the algae naturally by finding the right balance of light / nutrients. Algae itself is not harmful to fish - its only the owners that woryy about it.
 

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