My First Real Algae Problem In 15 Years

[Troutstudio]

I have a 4 foot tank with relatively few fish, kept out of indirect light. My plants have always had to be cut back every few months! Recently I removed most of my driftwood, which was old and very soft. I started getting this algae. I can't get rid of it. I bought new flouro tubes. I change water regularly. I feed very sparsely. Just not sure what to do. Blackout? I have a lot of fish keeping experience but this is not a high tech tank. Any advice much appreciated. Normally I barely ever have to clean my fish tank and it gets comments all the time. Now it's a mess.

 

[Chad]

This is just a guess but I think that when you removed the driftwood you removed large part of your bacterial filtration as well. Driftwood is quite porous and unless it's high in tannins it's great at harboring bacteria. Much like liverock in a reef tank it can be dense enough to create anoxic zones which actually promote the growth of denitrifying bacteria. If this is the case then removal of the driftwood would cause a rise in nitrates.
 
There are certain kinds of algae and cyanobacteria that actually thrive in higher nitrate environments. An unchecked increase would promote their growth, I believe even in a planted tank since it would occur so quickly.
 
The other school of thought is low Co2 but given the removal of the driftwood preceding the algae growth I lean toward the nitrates.
 
Again...at this point it's my best guess. It's a guess because I don't know much about your tank only that you had no algae, removed driftwood, then had algae.

 

[daizeUK]

I'm slightly confused.  All the nitrifying bacteria that I know of in freshwater tanks are oxygen lovers.  I thought that anoxic zones were generally bad because the sort of bacteria that thrive there produce nasty waste products (and aren't particularly efficient nitrifiers).
 
Can you explain why there would be a rise in nitrates if nitrifying bacteria are removed?  I would think there would be a rise in ammonia and nitrite, but since nitrates are the end product of the nitrifying process in FW tanks then they shouldn't rise any further.
 
One thing I have heard is that disturbing the substrate in well established tanks can kick up a lot of decomposed organic matter which releases an ammonia spike and some types of algae will feed on that.
 
Can you test your water to see if anything is out of the ordinary?

 

[Chad]

Not nitrifying bacteria, denitrifying bacteria. My theory is he removed the denitrifying bacteria which would lead to an increase in nitrates which would lead to an increase in nitrate loving algae and/or cyano.

 

[daizeUK]

I see!  I didn't think we got any of those type of bacteria in freshwater tanks.  I never knew they could colonise driftwood, that's interesting.

 

[Chad]

It's not common to have them in FW tanks as the conditions for their growth seldom exist. But deep inside a piece of driftwood I believe they could. They are common in FW lakes.
 
As a side note they have found species of denitrifying bacteria are oxic.

Anyway...that's my guess as to cause.
 
Treatment would be to remove the nitrate from the water through frequent and deep water changes.