As for little schooling fish that can encourage cardinal tetras to school, in my 100 gallon 5ft tank, I had 30 cardinals, 20 rummys, and 20 espei (rasboras). Back when the tank had no plants to sparsely planted, rummys, espei and cardinals would all school together. Even after months, which the cardinals should surely have became comfortable and just hovered around. But with the active schooling fish, the cardinals joined right along playing with them most of the time. However once I started getting into planted tanks, the more plants I would add, the less schooling activity would take place among the fish. Sure enough once heavily planted, the once 24/7 (seemed like) active schooling fish were pretty much only hovering now. After doing plant trimmings, reducing plant mass, fish activity would increase. So basically, the more plants, the less active fish. Not everyone experiences this, or at least they don't report so, or they don't notice the behavior/activity change. I for one, observe fish behavior quite a lot and I have concluded that the more plant mass, the less active the fish are (pretty much all fish species, not just schooling/shoaling fish). I am not the only one who has noticed this connection. Anyways, I could go on and on about that (already done so in past posts).
So what I am saying is, in my experience, active schooling fish did entice cardinal tetras to actively school (not out of fear/stress). Though that active schooling may be hindered by more plant mass (even with open swimming space). So pretty much it's not a guaranteed thing. Cardinals might not actively school. With enough plants, even active schoolers like rummys and rasboras might not school (as I've experienced). But yes, for recommendations on little schooling fish, I would say rummy noses and rasboras are best (Espei are a favorite). Personally much prefer Espei rasboras over rummy noses for quite a few reasons, but both are great tight active schoolers. Haven't personally kept Black Neon Tetras, but I hear they can school fairly well (occupy upper half of tank).
I haven't kept Apistos yet so I'm of no good advice on those. Haven't made up my mind on which species I would get either. So many nice colors/patterns to choose from. Have kept ram cichlids though.
For algae eaters, I would recommend Reticulated Flying Foxes (Crossocheilus reticulatus). Related to true Siamese Algae Eaters (Crossocheilus siamensis). They eat many pesky algae types that many other fish won't touch, just like the SAE reputation. Mine are around the 4" mark and they still eat algae and are not aggressive, unlike some people reporting their SAE becoming a little aggressive and no longer eating algae (just fish food). So in my experience with them, they have the great algae eating reputation SAE, only better. Plus you can't misidentify reticulateds as SAE commonly are.
Some people might recommend Otocinclus (Otos), which are a peaceful algae eater, but some report them only eating brown algae (diatoms) and soft green algae, and not eating any fish food (not even algae wafers). They do like fresh vegetables though. Some people's otos do eat fish food though. But it's always wise to assume the lesser, so if you want to keep them, make sure to provide enough food for them so they don't starve. The SAE/reticulated above, will eat fish food, so no real need to worry about those starving to death.
Thanks for mentioning your experiences with the fish you have kept.
