So, I have this idea, but don't know how it would work or the best way to go about doing it.

What if I wanted to take maybe a 3rd of my 29GAL tank and change the substrate to a finer sandy type bottom and leave the rest small gravel. Just thinking about giving the kuhlli loaches a place they would enjoy. Is that a good idea? And if so, how do you do it with water already in the tank. Never messed with aquarium sand before. I was thinking do it in conjunction with a water change; put the sand in a cup, wet and press it a little, then dump it where I want it. We want to add a few more live plants anyway.
Whadda ya think?

I thought of something else I was wondering.

I've got these 6 tiger barb eating machines...the 3 gold barbs do fine competing for food, but I'm a little concerned about the kuhlli loaches. I know I need to get some food that sinks quickly, but I still think the tiger barbs will devour anything ya stick in there. I don't want the loaches to have to rely on scavenging for algae all the time.

I know the loaches are more active at night, so I tried feeding them while the barbs were asleep. I managed to get food in there without disturbing the sleeping barbs, but after a few secs they smelled it and pounced on it. So what do I need to do?

feed the loaches some wafers and shrimp pellets. they sink fast and the barbs wont bother them much especially after dark.