How big is he?? It's most likely won't get to much bigger unless if it's moved to a bigger tank. I had one in a 75g and he was about 14"-16" long and I only dropped in some type of bottom feeder food on occasion. They don't grow too fast though.

 

The same thing that promotes growth in every type of fish. Good environment including but not limited to room to move, and stable water. A varied balanced diet (more proteins and fats when fish are younger). Basically a stress free life and a full stomache.

 

it depends on the type of pleco he is. Some plecos are mainly alge eaters and some meat eaters depending on speicies. If it is a common pleco then alge is a bigger part of diet. Plecos also need boggwood in their diet to help them diegest. I offer my plecos a little of everything. I switch it everynight. One night alge one night shrimp pellets next night cucumber next night frozen brine. ect. A well rounded diet is the best for any fish including plecos.

 

it depends on the type of pleco he is. Some plecos are mainly alge eaters and some meat eaters depending on speicies. If it is a common pleco then alge is a bigger part of diet. Plecos also need boggwood in their diet to help them diegest. I offer my plecos a little of everything. I switch it everynight. One night alge one night shrimp pellets next night cucumber next night frozen brine. ect. A well rounded diet is the best for any fish including plecos.

Is there an echo in here?

 

Well even with a really good diet and stable conditions a common pleco or any of the larger plecos won't reach it's full potential in a 29g.

 

I agree with everything mentioned above.

 

The only advise I have you may not like, but here it goes anyway. Move the shubunkins and comet to a pond, then a 29 gal will house one or two fancys ok. The pleco will probably grow slow and won't reach his full size in a 29 gal where he has to compete with goldfish aka waterhogs. Unless you throw some food in after lights out, the goldfish will gobble everything up before the pleco even knows it's there. Even that may not work. My goldfish "wake" up in the dead of night if they smell food.
I had a rubberlips in with them for a while and had to place the algae wafers and shrimp pellets in the back part of a cave that only the rubberlips could get into. He was brave enough (or hungry enough) to be out in the open all day and fought the goldfish over zucchini slices but not all plecos will do that.

 

Awesome, thanks for the advise everyone, I will definitely use it

 

Cucumber is a great food for plecos since other fish will barely pec at it. Other catfish mAy have a go but plecos gobble it up in no time

My plecos actually swim to the top of my tank to grab flakes and bloodworms