My Grammode male killed the female with in the 1st day of having them. I should of divided them. O well, lesson learned. GL with the pairing, they grow SLOWWWW!
I would suggest adding some other fish in there for them to harass. I have a pair that are slightly smaller than the sizes you have stated in a 125, and the male was being abusive. They almost killed a 4" female carpintis and are beating on a couple of 4" marbled convicts. They are one of the more aggressive fish I've kept.
I would slap a black background on that tank. The grammodes look a little pale, which is no doubt simple a matter of lighting, substrate and background (or lack thereof)
Other then that they look great, and i wish you the best of luck with them. They are awesome little beasts. Mini-dovii for sure
PowerGlo tubes work wonders with Grammodes. The substrate you have is fine, and since you're getting a background on, nothing other than the tubes can be done. But after those upgrades you won't need anything else done. Your grammodes will look awesome