Thick Green "slime" on water surface... dying fish - Tropical Fish Keeping - Aquarium fish care and resources
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post #1 of 26 Old 06-02-2012, 12:16 AM Thread Starter
bigehugedome's Avatar
Thick Green "slime" on water surface... dying fish

Hi all,

So I worked from home today, and while looking at my tanks I noticed the ember tetra in my 10 Gallon were not active, and hiding under my plant leaves. I thought ich, because I got ich in this tank before and they were acting the same way, but i didnt see spots on them.

For whatever reason idecided to lift the whole lid off the tank and I saw this thick green slime on the surface. I did a water change this past monday, so only a few days ago, and changes the aquascape around so this slime was not there at that time. I netted it out and flushed it. The fish hid all day so I checked water parameters and everything was normal. I tried to feed them a little early and they all came out to eat, then hid again. I went out for dinner and came home found a dead cory and everyone else still hiding.

I did add driftwood to this tank on Monday. I had the driftwood in it before but it leached tannins so bad that I took it out for a few months (the water was dark brown in about two days). I finally got a pot and boiled it the past 3 weeks for proably a total time of 5 hours, when the water was pretty clear. I did not have this wood in the tank when i got ich last time. I just had to remove it because the water got so dark so fast.

I also did not like my sponge filter, so i bought another one, and had them running side by side to seed the new one for the past two months and removed that on Monday as well.

My question is what do you think this slime is, and what do you think could have caused this random death.

P.S. I did a 30% water change and took out the wood for now. I see no mold/fungus on it.

Another thing to point out is I have MTS and the first day i put the wood in they all came out of the sand and went all over the wood, even during the day, and the corys browsed it for a few days.

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post #2 of 26 Old 06-02-2012, 02:59 AM
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You know it kinda looks like cyanobacteria. I know it floats or can float in calm water but didn't know or have heard of this in aquariums? When this happens in ponds or near shorelines it can be thick and actually take oxygen and nutrients out of the water for its own use. Maybe (just guessing here) this is what happen in your case? Or I could be crazy as it is 4am LoL

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post #3 of 26 Old 06-02-2012, 06:11 AM
Not enough water movement and/or filtration in the tank?
Too much light?
Neglected routine weekly water changes?
High nitrates?

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post #4 of 26 Old 06-02-2012, 07:22 AM Thread Starter
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Maybe not enough water movement due to the new filters positioning and the floating plants. Allthogh when the slime is not there the plants do move around due to the current.

The light schedule did not change so while this could be the issue it's weird that the slime was never there untill 3 days after the last waterchange.

Not neglecting routine water changes. Done everybody Sunday or Monday night.

Nitrates between 0-5ppm
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post #5 of 26 Old 06-02-2012, 09:24 AM
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have you added any fertilizers in the water by any chance? because this looks like eutrophacation. its when there are fertilizers present in the water and a large algae bloom over the water appears..

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post #6 of 26 Old 06-02-2012, 11:50 AM
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That is cyanobacteria. I usually see it near the surface, attached to floating plants, first, but it can float like this too. In fact, I just recently had this in my 70g.

Cause is organics, in the presence of light. Blackouts will temporarily reduce it but it will continue to occur until the organics issue is resolved. I've had this occur simply by not cleaning the canister filter sufficiently (=too infrequently). Any increase in organics (which can be due to fish load, dying plant matter, overfeeding, over-fertilizing, not cleaning filters/substrate) may be responsible.

Do a water change, half the tank (assuming parameters are equal) with a good siphoning of the surface to remove the scum, rub it off plants, etc and siphon it out, vacuum the substrate; rinse the filter media.

Make sure the light and nutrients are balanced. I've seen this in tanks near windows since they get more light.


Byron Hosking, BMus, MA
Vancouver, BC, Canada

The aquarist is one who must learn the ways of the biologist, the chemist, and the veterinarian. [unknown source]

Something we all need to remember: The fish you've acquired was quite happy not being owned by you, minding its own business. If you’re going to take it under your wing then you’re responsible for it. Every aspect of its life is under your control, from water quality and temperature to swimming space. [Nathan Hill in PFK]
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post #7 of 26 Old 06-02-2012, 02:10 PM
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I really hope your remaining fish recover well. I've never even heard of this tank problem

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post #8 of 26 Old 06-03-2012, 06:29 PM Thread Starter
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Lost another cory today. They looked fine yesterday and when I woke he had "white stuff" on him (see pic 1). Went out for 3-4 hours and came back and he was dead. He looked like he was wrapped in a spider web. White fuzzies/moldy looking. Not sure if thats just a rotting fish or signs of something else. No snails on him or anything. COulndt get a good pic of this, he just looked white.

Not sure why this is happening. I can only blame the wood, allthough i dont want to because I bought it for this tank! I thought i was playing it safe by boiling the wood now this happens. As for too much organics/ inbalance, not sure what it is. I seeded the new filter before i removed the old one. Did a 50% change ( i do 20%-30% every week) because i was re-aquascaping, then added the wood. Light timing has never caused an issue, and this is the largest amount of plants i ever had in this tank so if anything i would think that this algea would be less of an issue now. It has not yet returned.

Looked at a tetra and saw this now. I dont see any spots on them that look like ich, just this (pic 2). the white stuff is like hanging off him

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post #9 of 26 Old 06-03-2012, 08:31 PM
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The fish is not related to the wood. I will PM Dawn and ask her to kindly take a look here. In the interim, you might want to post full tests for the water (GH, pH, temp, ammonia, nitrite, nitrate), fish in the tank, etc.

Byron Hosking, BMus, MA
Vancouver, BC, Canada

The aquarist is one who must learn the ways of the biologist, the chemist, and the veterinarian. [unknown source]

Something we all need to remember: The fish you've acquired was quite happy not being owned by you, minding its own business. If you’re going to take it under your wing then you’re responsible for it. Every aspect of its life is under your control, from water quality and temperature to swimming space. [Nathan Hill in PFK]
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post #10 of 26 Old 06-03-2012, 11:54 PM
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I agree with Byron thus far and I don't think the cause of the fish illness is directly related to the cyano/algae mess you had at the surface of the tank, however... that and the wood itself could be a contributing factor.

Can I ask what kind of wood this is? Do you have a clear photo of it? Where did you get it from? (store bought aquarium safe, outdoor scavenger hunt, garden center, etc?)

I am going to need current water parameters for ammonia, nitrite, nitrate, pH and water temp, and to know if you have a quarantine tank? I'm also going to need a list of all fish/inverts in the tank (and how many of each) as well as what foods you are offering, how much, and how often. What chemicals do you add to this tank? (please include brand of water conditioner, any fertilizers, etc. that go into this tank)

Is there any way to get a clearer photo of the affected fish? I am suspecting this is fungal but cannot offer more than a suspicion based on the last photo.

In regards to driftwood... anytime we add wood to an aquarium there is some level of risk, even if it is bought at a pet store and listed as aquarium safe. There are many different types/species of fungus, parasites, and even algae that can live inside of driftwood and boiling or even manufacturer treatments (usually heat, sometimes chemical or both depending on the company) can't guarantee they will kill everything. The more dense the wood the more risk involved that something inside the wood may have survived. All it takes is one spore of fungus to start a problem when conditions are right for it to thrive. These spores can lie dormant for years and then suddenly one day when the conditions are right... boom, you see a problem. The same applies for parasites and their eggs. Your description of the heavy tannins in this wood tells me this is pretty dense and likely either Malaysian drift wood, welaby wood, or something similar, which are known to carry heavy tannins. I am going to take a guess here and suggest that this piece of wood seems heavy for its size?

Wood can also contribute to organics in any aquarium regardless of the amount of maintenance, filtration, etc that is being done. Wood rots, often times from the inside out where we can't see it... and those spores and insect/parasite eggs can do the same thing... After reading all of the info in this thread I am going to suggest you not put this piece of wood back into your tank. If you have done so already, then I would suggest removing it and not using it for an aquarium again. Soaking it, boiling it, etc. isn't going to do any good if the problem is coming from within the wood, which is very possible and there is no way to predict such a thing. Testing it in another aquarium also can't always tell us everything it will do in a specific tank because as mentioned, many of these problems only occur when the conditions are just right, which may happen in 1 out of 1000 aquariums...

There are some wonderful artificial pieces of aquarium decor available that look like real driftwood but are made of resin. I would suggest you pursue one of these if you desire a piece of wood in your tank.

Once I have the info I asked for we will continue to sort out the problem with the fish and any medications you may need to help get them through this problem. The more info you can offer the faster and easier it will be for me to help you.

Dawn Moneyhan
Aquatics Specialist/Nutritionist
Juneau, WI
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