The question that needs to be asked is:
What kind of filtration do you have?
The proper solution lies with the answer to this question. Since the tank is a 29g, we have to assume the possibility of an under gravel filter. That will complicate how you change the substrate and whether you can add fish at the same time.
For what it is worth, it is a bad idea to add new fish at a time you are stressing the system as a whole. Give it time to settle and to allow you to observe if there are any complications. The process is going to be stressful on your fish and adding new ones won't help any.
An easy and clean way to do a 'fish in' gravel change is to syphon it out with the hose from a gravel vac (head removed). The debris will be sucked out with the gravel leaving the tank clear. Suck out as much as you can get out with 50% of the tank water. Refill the tank and continue the next day.
What kind of filtration do you have?
The proper solution lies with the answer to this question. Since the tank is a 29g, we have to assume the possibility of an under gravel filter. That will complicate how you change the substrate and whether you can add fish at the same time.
For what it is worth, it is a bad idea to add new fish at a time you are stressing the system as a whole. Give it time to settle and to allow you to observe if there are any complications. The process is going to be stressful on your fish and adding new ones won't help any.
An easy and clean way to do a 'fish in' gravel change is to syphon it out with the hose from a gravel vac (head removed). The debris will be sucked out with the gravel leaving the tank clear. Suck out as much as you can get out with 50% of the tank water. Refill the tank and continue the next day.
