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I am fighting an bloom of green algae that has really taken over my tanks. I found a couple of dead fish hidden in my bio filter that I didnt relize were there for a about a week, During this I had my tanks turn green with algae. my PH is 6.8. fish seem to be doing fine but it is just unsightly. I am using indoor grow lights and lexan fish tanks with rafts full of lettuce and basil. everything is growing great and fish are healthy.

My question is does anyone know how to get rid of it or at least slow it down so I can see my fish? Im sure it is safe for fish and plants but want to have cleaner looking tanks.

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Hello Kevin,

You will want to be sure to check your ammonia levels as dead fish will typically release a lot of ammonia which can be lethal to the fish.  That is probably also a primary cause for the algae as good filtration will help keep algae growth to a minimum.  As for the algae bloom, too much can eventually starve your system for nutrients and oxygen, unless you have fish that will eat the algae and hold it at bay. How much of your tanks are exposed to direct sunlight, or grow light?  Any direct light will produce algae over a pretty short period of time.  As for dealing with it now, you should be able to use a course brush to get it off the sides of the tank and then let the filtration system clean it out.  Over the long term, you will want to decrease the amount of light exposure to the water.  I have a small system that has clear glass in the front with a light in the back and it does produce some algae, but giving it an occasional scrub seems to keep everything clear.  Hope that helps! 


It receives 14 hours of grow light a day, but the majority of the surface is covered. I just teated ammonia and it is sitting at .25 ppm or less. I did notice my ph is up to 7.6 though

Ditto - If you don't' want it their scrape off as much as you can. Use a fine net to get as much as you can out so it doesn't decompose in the tank. Clean one half of your filters every couple days. Block as much light as you can from hitting the water. Might want to change out a little bit of water as well.

or just block as much light as you can from the water and most likely resolve by itself. If you do that make sure to check ammonia and nitrite levels daily till it clears up.

I checked the tanks and most of the algae is not on the sides of the tanks it is more so in the water itself. The water color is dark green. Some algae on side but very little.

Greenwater is almost always too much nutrient, combined with too much light hitting the water. It's hard to nail down with ammonia and nitrate testing, as the free-floating algae is thriving on the nitrates in the system, consuming what you would normally have show up on a nitrate test, producing a false low result. Cut back on the feeding, bump up your solids filtration, and take what my seem like excessive measures to prevent light from hitting the water. At this point a water change wouldn't hurt either. An additional place to look for advice would be a planted aquarium forum, as their systems operate similarly to ours. I'm battling greenwater on one of my indoor tanks (not an AP setup). Hard to limit your feeding when you've got a bunch of hungry fish you're trying to grow out.

ok so a week and a half later and my green water is still prevelant. I blocked the majority of light from hitting the water and havent fed my fish for a week. still water as green as ever. Ph sitting at 6.0. lettuce and bisil look fine and fish dont appear to be stressed. but hate the green water. I also did a partial water change a week ago.

 any further ideas on clearing it up?



I keep string algae away with a small amount of sea salt. 

In my 1300 gallon pond I use about 10 pounds of salt to bring the salt concentration to about 0.3% or 0.5%.  

Maybe your algae is out of control, but I let the other short green algae grow in my AP system.  The fish like to eat it.  Luckily I've never had sting algae in the AP system.

Not sure how your tanks are set up, but you could try freshwater mussels/calms. They are filter feeders and are rumored to work wonders on greenwater in freshwater aquarium systems. If you don't have substrate for them to dig into, just take a plastic jar and drill enough small holes in the top half to allow water to pass through freely (think Swiss cheese), fill the bottom (un-drilled portion) of the jar with medium/fine sand to give the little guys a place to bury themselves without fear of harassment from the other occupants of the tank. sand depth only needs to be about 1" - 1.5".  Make sure to place the jar near/in the path of water movement and not in a quiet corner of  to the tank, to ensure constant flow through the clam cage. I'm trying this in one of of my indoor aquariums currently. Currently too soon to tell if it is working. I'll try to post a photo tomorrow.

one other thing. if you do decide to add clams, be sure to start feeding them once the greenwater situation is resolved or remove them from the system. decomposing clams are little ammonia bombs and will throw off your chemistry.

Run a UV filer on it for a week. Some of the better pond/aquarium shops will rent it out. Make sure to clean it well before using.


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