are you referring to that old myth that copper is absorbed by the silicone or the glass? That's nonsense and has been de-bunked a thousand times.
To the op:
I've treated pps with cu a few times. I kept cu at the low end, cupramine at .35ppm, with no problems. Treating fish in any dt is very iffy at best. Lr & substrate constantly absorb & release cu (and probably cp) into the water column and this makes proper dosing almost impossible. Just a minute of cu below the therapeutic minimum can ruin your efforts. Get a qt/ht, try craigslist. Imo & ime; this hobby would be a nightmare, long-term, if i didn't have one. A qt/ht is a necessity, not just something nice to have.