Hello Paul,
Yes, I think you´ll be ok with one Vortech but instead of placing it in the second Tunze´s spot, I would consider putting her in the right side, also against the wall and in the middle of the glass to sweep the tank from right to left with a downward flow and from left to right with an upward flow. The right-side Tunze, with the position you have her in the pics, would create a backwash in the Vortech´s flow and in the front glass that could help getting some circulation in the left side of the overflow where the second Tunze was.
Just a suggestion to try getting all the potential of the pump.
530€ for a Gemmatum? It is less expensive than getting them here which they run for 600€ at least ( on those rare occasions that TMC Iberia has them), though 150€ is where I draw the line when paying for a fish, no matter how rare they are. :lolspin:
I suppose your lfs fish come from TMC too. Am I right?
Regards,
André