Yikes! Bio crash?

Gosh, it seems like the fun never stops, eh?
This post started as a diary entry, and I decided it
might be useful to get the opinions of others here.

Last weekend, _two_ of my three tanks seemed to crash:
measurements showed ammonia in the 1.0 range, with zero
nitrites and minimal (but detectable) nitrates.
I surmise a complete bio crash. I'm searching for possible
causes, and wanted to share the observations and maybe get
a clue I'm overlooking.....
Here are my case notes thus far;

- these two tanks almost always get maintenance together,
and usually in the same order: 18g then 20g;
- by contrast, the 55g is maintained on a separate schedule,
and didn't crash;
- over that time frame ( 10-14 days ago) I was experiencing
a rash on both forearms -- probably shingles -- and was
treating the itch with various combos of Lanacane (which is
benzocaine + benzethonium Cl + a pot load of inactives),
a topical antihistamine (diphenhydramine HCl + Zinc Acetate),
and/or a topical hydrocortisone ointment.
- I tried to make sure to wash (and carefully rinse) my hands and
forearms each time, aware that I was carrying weird chemicals,
but was it effective? did I forget? Did I just happen to be
cleaner each time I did the 55g?
- same time frame: I started making my own eclipse filters for
BOTH these tanks (but not the 55) using polybat, some
blue floss, rubberbanded onto an empty eclipse filter frame;
- the purple and blue rubberbands (from vegetable bundles)
seem to stink like chemicals after being used on these
filters.... _don't_use_them_anymore_!;
- started using Amquel+ (also still have some regular Amquel
in use), but I suspect it's been in all three.

I guess what all that drivel means is there's only one factor
that's unique to those two tanks: the stinky rubberbands.
Does anyone have any info about this phenomenon?
The odor is sharp, vaguely familiar (acetone? some petroleum
byproduct?) and distinctly non-aquatic.
(I suspect there's a 50-50 chance I contaminated the tanks
with my drugged forearms, but I would suspect that would
only happen to the FIRST (18T) tank...repeatedly dipping
my arms into it should have diluted the stuff before I started
on the 2nd one, yes?)

Thanks,
Gunther

PS: jobless rate is still nasty high here in Silly Valley :-|
I'm probably moving, but have no idea how or where.....