Evil Biofilm Attack - SOS! - El Natural

Dustymac · 05-01-2008, 02:31 AM

This is a weird one. For the last few weeks I've been battling a surface biofilm which I suspect is starting to kill the floating frogbit. It seems like every day I siphon off half of it and the next day it's covering the whole surface again. Now the frogbit is starting to die off, either showing rot in the petals or a checkerboard of chlorosis. I have duckweed in the tank, too, but that doesn't seem to be affected.

The particulars:
45 gallon tank
gravel substrate
heavy fish load
heavy plant load
ph=7.4
gh=8
ammonia = 0
nitrites = 0
nitrates = 20-100 ppm
about 1.75 watts per gallon.

There is a canister filter but I removed everything but the floss months ago. The pond snails in the tank don't want anything to do with this stuff. When I first added the frogbit to combat algae, it went growth crazy, but the cut in lumination caused some of the lower stem plant leaves (ludwigia repens) to die off, adding DOCs (I guess) to the water column. None of my other tanks have this problem. Anyone have a clue?

Jim

dwalstad · 05-01-2008, 05:03 AM

I doubt bacteria are killing the Frogbit. Rather, the dying plants (first Ludwigia stem plants, then the floating Frogbit) released DOC (dissolved organic compounds). Scientists have shown that dying plants release a LOT of DOC. This DOC release probably stimulated your surface bacterial biofilm.

Your Frogbit may have grown well until its growth was limited by some other factor (iron would be my first guess). If your Frogbit is yellowish, especially the new growth, then iron-starvation may, indeed, be your problem.

You say you have a gravel substrate. If there's no soil, then you've got a major disadvantage to work around. Without soil, submerged plants don't grow well enough to compete with algae. Floating plants can help in this situation, but you might need to routinely add chelated iron fertilizer to the water. Or you may need to do water changes to remove excess DOC. Or just manually remove the surface biofilm. I'm not sure what the solution is.

In any case, I'd be glad that your duckweed is doing well.

Dustymac · 05-01-2008, 07:50 PM

Diana,
If course you're right. I did an iron test on the water and it showed a big zero. It's funny how different plants need different nutrition to thrive. In the same gravel are Amazons and Anubias which are growing fine.

About the gravel, unfortunately I set this tank up (and another) before reading your book. That's not a mistake I'll ever make again. Right now I have two 10 gallon soil substrate test tanks more than six months old and everything about them is great! And this past weekend I started assembling a 55 gallon NPT. It's going in the window and will get a little direct sunlight - something I never would have done before "Ecology of the Planted Aquarium".

Finally, do you think the elevated DOCs will affect the fish or do I need to get them down?
Thanks!!!
Jim

Dustymac · 05-10-2008, 03:13 AM

Just an update. I took all the ludwigia out and any other detritus that might be contributing to the DOCs. I also removed all the Duckweed and Frogbit, vacuumed the gravel, scraped the algae off the glass and cleaned out the canister filter. Spotless.

Then I siphoned off about a gallon of water every day, removing about 90% of the scum. Within 12 hours it was back again, and all the water changing caused a diatom bloom. With no floating plants, I got an algae bloom, too. On the up side, the film has a pearlescent sheen that's really quite attractive.

So, I put the Duckweed back and adjusted the spray bar to stir it into the scum, and hopefully keep it broken up. That worked for a couple days. Now the Duckweed is segregated and compacted into rotating patches and is clearly starting to die off like the Frogbit. I've even tried transplanting the biofilm to my other NPTs to see what would happen but it just doesn't take. Thankfully, the fish show absolutely no signs of stress.

I'm thinking it's time to throw in the towel on this aquarium and convert it to a NPT.

dwalstad · 05-11-2008, 02:52 PM

Quote:

Originally Posted by Dustymac

Diana,

Finally, do you think the elevated DOCs will affect the fish or do I need to get them down?
Thanks!!!
Jim

DOCs (by themselves) shouldn't hurt the fish.