Hair Algae

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megatronmo

Aquarium Advice Newbie
Joined
Jun 8, 2025
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Location
ohio
I have a 10 gallon freshwater tank that I’ve had for about 3 months. I started with 2 Tetra Glofish. Algae growth was getting insane so 2 weeks ago I added 3 Otocinclus. The Otos have done an amazing job cleaning up the soft algae that was on the glass and hard surface decor. However there is still a large amount of hair algae on the fake plants. I added a clump of Java Moss at the same time as the Otos and it’s covered in algae now too. My Tetras seem to be eating less and there’s an abundance of uneaten food in the substrate. I’ve been trying to remove as much as possible with vacuuming but it seems never ending. I feed a small amount of flakes, once a day (the pet store told me to feed 2x a day). Should i feed even less often? I don’t understand why there’s so much uneaten food. Yesterday, I manually removed some of the hair algae but I want to get to the root of the issue. It could definitely be excessive light, as the tank is in a room with many windows. I haven’t tested phosphorus levels but our water is hard, so i could imagine it’s likely high. The ammonia/nitrate/nitrate levels have all been good but I’ve been doing a good amount of water changes with my cleaning attempts. Should I try a blackout? How do I keep this algae under control? I’m at the end of my rope.
 
Algae is caused by excess nutrients and/ or light. From what you have written it seems to me you know what the root cause is.

You want the aquarium as far from natural light as you can reasonably get it. So the far side of the room from a window or keep the curtains/ blinds closed. To give you an idea of how light levels fall as you move away from a window. Outside in the shade 10000 lux, inside on the window will 500 to 1000 lux, 4m away from the window 20 to 50 lux. So you could easily have 10 x more light next to a window compared to on the other side of the room. This difference in light intensity isn't apparent to your eyes as they are good at adjusting to different light levels, but 50 lux compared to 500 lux is a massive difference when it comes to photosynthesising.

And you want to limit the length of time the aquarium light is on to 6 to 8 hours a day.

Blanking out the aquarium completely will kill off your algae, but if you dont address the cause it will return. Blacking out will also kill your plants, and will cut off the source of food for your otos.

You want to be feeding as much as the fish will eat in 3 minutes. If there is leftover food after 3 minutes you are overfeeding. Or feed a little bit less twice a day. To give you an idea, most fishes stomachs are the size as one of their eyes, so 2 tetras that might only be 3 or 4 flakes per feeding. Tetras don't typically scavenge food once it's settled on the bottom, so consider feeding a little at a time so they have chance to get at all the food before it drops to the bottom, then feed a bit more, until your 3 minutes worth is gone.

What is a typical water change schedule? How much, how often?

What is a typical set of water parameters?

Can we also address the tank size and species? GloTetras are GM black skirt tetras. These tetras are social fish and need to be kept in groups. Keeping just 2 fish of this species is going to be stressful for them and stress can manifest in a variety of ways. They might hide, they might get aggressive, they might just make the best of it, or they might not eat. A 10g aquarium is on the small size to accommodate a small group of black skirt tetras.
 
At this point I’m questioning whether I should use my light at all? Even when the blinds are closed, there are windows near the ceiling that let in light.

I feel like they could be more stressed since the addition of the Otos. They had been eating fairly well prior to that.

I typically do a 25-40% water change 1-2x weekly.

I just tested the water and these are typically the results I get.

Yes the tank is small. When I went to the store to get fish, I had fully intended to get Danios. But of course, my son picked out the Tetras and wouldn’t budge. I had asked the pet store employee how many would be appropriate for that sized tank and he advised that I get 2 and see if I could keep those alive.

Fast forward to now, when my son couldn’t care less about any of it and I’m just trying to do my best for the little guys.
 

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I speak as a former pet shop retailer, when it comes to keeping animals, any animals, as pets, children should have very little to no say in the matter. These are living animals that have particular needs which need to be met and that far exceeds the understanding of most every young child. I wouldn't sell a fish tank to anyone for a child under 6 or 7 years old. They just don't handle the needing to wait for certain things to happen to make the tank safe for the fish. Speed kills more than it doesn't. I don't know how old your son is but he seems to fit the reason I explained why young kids shouldn't be making pet decisions. :(
Your pet shop did not do you right by selling you Black Skirt Tetras ( The glo- tetras are a version of the Black Skirts) for a 10 gallon tank. If you could return them or trade them in, I would so that you could get fish better suited for a 10 gallon tank. As explained, the hair algae is the result of too many nutrients coupled with too many hours of light. Combine the two and you have problems. Eliminating one of them reduces the problem while eliminating both of them solves the problem. If you can't eliminate both, there are some fish species that eat hair algae in particular. Otocinclus are not one of the species. They prefer the biofilm type algae which is why your hair algae problem still exists. A good fish for eating hair algae in a 10 gallon tank is the Florida Flagfish. The issue would be if they would live with the Otos as the tank is small and Flagfish can be a little hogish on having enough room. But first off, I'd have your water checked for phosphates and iron as these are often the cause of hair algae. You won't solve the problem if you continually feed the beast with water high in iron or phosphates during the water changes. As Aiken explained, blacking out the tank will not stop hair algae from coming back if the root cause is not addressed. For now, plan on manually removing as much as possible until you get either fish or shrimps that eat hair algae specifically. Your tetras reducing their feeding sounds like they are stressed and the tank size may have a lot to do with that as much as the lack of a school. This is why they should be traded in IMO. It's hard to not overfeed such a small amount of fish and that's part of your problem. Adding more fish with the Glo-Tetras may be a problem in a tank that small. Having a tank with the right fish can help solve your issue.

Hope this helps. (y)
 
While your ammonia level is stating "safe", there is detectable ammonia in your test which will be supply nutrients to algae growth. While a low level of ammonia might be considered safe for fish, it's not desirable and it should be zero.

Mention of ceiling level windows isn't ideal, as high windows allow much more light into a room and allow it to penetrative much further. I would consider the aquariums position, and if you cant relocate it you should look at something that will eat hair algae. The flagfish Andy suggests sounds like a good idea.

Turning the aquarium light on or off probably won't make much difference to light levels in the aquarium if there is natural light present, but if you can see your aquarium OK without the aquarium light on, then no real harm in turning them off. You have java moss that will benefit from having the lights on, but I've kept java moss alive in an unlit aquarium before just fine.

And I'd really consider if the aquarium is something you want to put time and effort into if it was for your son who is no longer interested. If you want to continue and you are no longer tied to what fish your son wants trade the GloFish in. Most danios, which you originally wanted are a bit too big and active for a 10g, but glowlight danios are smaller and would better suit the aquarium size. I really like glowlight danios, they are prettier fish than zebra danios for instance, and a lot less prone to genetic defects.
 
Hello mega. Small tanks will be a challenge for even the most experienced keeper. The water is constantly in a state of change and this is typically fatal to whatever lives there and an opportunity for plants to either die or thrive. Your best chance of success in this hobby is to upgrade to a much larger tank, at least 30 gallons. 55 is likely the best size. Otherwise, in my humble opinion, you'll continually be frustrated with less than optimum water conditions.

B
 
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