Ah, that's nice. The bigger tank will be a permanent solution.
I wouldn't worry about the diatoms for now, especially if the plan is an upgrade. You can still try increasing the surface movement and try to feed less while the fish are in the 29G. A photos plant would also help with the diatoms , and the water quality as it will draw ammonia before it gets available to unwanted organisms and algae.
Filtration is limited to the amount of oxygen in a tank, providing the turnover is sufficient, which it is in your case. There is obviously abundant ammonia, the diatoms being an indicator. So the solution lies in one or a combination of the other things mentioned.
I wouldn't worry about the diatoms for now, especially if the plan is an upgrade. You can still try increasing the surface movement and try to feed less while the fish are in the 29G. A photos plant would also help with the diatoms , and the water quality as it will draw ammonia before it gets available to unwanted organisms and algae.
Filtration is limited to the amount of oxygen in a tank, providing the turnover is sufficient, which it is in your case. There is obviously abundant ammonia, the diatoms being an indicator. So the solution lies in one or a combination of the other things mentioned.