Biofilm!!

[Zoe]

So I am having some issues with biofilm on my tank. It's so think that if I blow on it, it doesn't separate.  I have a poppy glass pipe which does agitate the surface but it doesn't seem to be breaking the biofilm. I'm starting to worry about O2 levels at this point.

Every day this week I have skimmed it off. Every day it has come back. I have cut back on feeding, dosing, and even water conditioner (I wasn't really measuring before and I am sure I was using too much) this week to no avail.

I have always had biolfilm but it's never been so pervasive before. Nothing has changed except I cleaned my filter two weekends ago (just rinsing out the media in aquarium water).

My tank is lightly stocked. Specs:

20g tall
Satellite FW LED light (I consider about medium lighting)
Heavily plantec but mostly mosses and pellia and such. Crypts, HM, as well
3 oto cats, 5-6 adult badis and about a dozen fry, 1 sparkling gourami, 10 micro rasboras, lots of neo / crystal shrimp
I feel live microworms and some frozen stuff (daphnia and bloodworms) every day, an occasionally an algae pellet
I dose about 1/3 cap of excel every 2-3 days
No CO2
API leaf zone, about 1/2 cap every 1-2 weeks
Eheim canister filter, 2217 I think? The one rated for about 40 gals.

I know the answer is usually "surface agitation" but, I already have some and it isn't helping. I also have a very minimalistic tank (external heater, glass pipes) so I'd rather not put a powerhead or airstone in there.

Alternatively there is something like this:
http://www.aliexpress.com/store/product/ADA-style-nice-quality-13mm-17mm-for-12-16mm-16-22mm-water-hose-aquarium-filter-glass/1487206_32297574260.html

But I am scared it will break, as I have heard of that happening before.

Any ideas?

[lucius]

You can try a Fluval skimmer for now to see if you like it.  I use one in my 75 gallon connected to an AC110 and have no biofilm at all.