How safe is black water?

No, really.

With Jan's encouragement I built a skippy filter. Took a week to clear
the green water, but it worked! Last week tore the back off the
waterfall (http://artships.com/pond.php). Installed the skippy filter so
that the tub's spout would run right over the waterfall. Works!

Rebuilt the rest of the waterfall around the tub. Left the top over
the skippy open so I can stick plants in there, but will put rocks around
the edge. Note, "will". Until then, I've applied Great Stuff aerosol
styrofoam between the edge of the tub and the surrounding rocks. Couldn't
find the black kind, so I painted the exposed styrofoam black. Used a
latex enamel. Looked great.

Irrigation system went off on schedule last night. Washed some of the
almost-dry black paint off the styrofoam and into the pond.

*expletives*

Six hours later, goldfish still seem healthy and happy. Thinned latex
paint is thinner than algae, but will the skippy filter still snag it all?
Will the pond clear? And Latex paint is much less caustic than, say,
lacquer, but with no intervention on my part will the fish still swim in
this continuum or float to the top on their way to the next?

Sucks to be me, today. Or one of my hapless goldfish.

John