Those plants might look after a trio of guppies but an rtc would need a massive amount, even that tank filled to the absolute max with plants, plant substrate and co2 injection ain't gonna do diddly squat for a growing rtc.
As the other poster said, it doesn't matter as he will be in the 1000 gal in a few months.
What will you out him in eventually, when he out grows the 1000?