I will invest in a powerhead and or a skimmer. My nitrates are a pain in the butt. My water source in 40ppm I put seachem denitrate in my filter hoping this would help.
As for feeding I use flake twice daily 12hrs apart (small pinch) and on the night feeding I add 3-4 pellets in for the cory and the candy stripe.
Once a week I will put a pinch of dry bloodworms.
Everyone has already hit in the main culprits, food and lack of surface agitation.
What brand of flake food are you using as that would be the prime suspect?
Seachem's De-Nitrate is a media for de-nitrifying bacteria to colonize, that process takes roughly 12 weeks for the media to be colonized enough to begin to see a difference.
You may try something like Chemi-Pure or Purigen or even both to help remove dissolved organics before they are converted by the nitrogen cycle thereby reducing the overall nitrate level.
They also do wonders for water clarification.
Aside from that, partial water changes are the only way to quickly lower levels, BUT,
80 ppm of nitrate, while high, is far from lethal or problematic for the fish.
In a planted tank you want about 10-20 ppm of nitrate anyway, IMHO.
ALSO since you scrubbed and boiled everything essentially killing all the beneficial bacteria except for what's in the filter, watch out for elevated ammonia levels and cloudy water.
You may have created a bigger problem for yourself.
Are there any places; supermarket or something, that has a water dispensing machine? My tap water has nitrate as well and I buy my fresh water from a machine @ .25 per gallon.
IMO, that radical of cleaning should ONLY ever be done if a pathogen is killing your livestock.
Algae is ugly, but not really worth that radical and risky of measures.
I have found that snails and pleco's do a pretty good job.
Good luck and keep tabs on all your parameters.
