I have two Plecostomus' that I bought together from what I've always thought was a reliable pet store (specializing in fish), called Moby Dick's Pet Store. I was told that one is a Calico and the other is a Lemon Drop Plecostomus. They were both very young and only an inch in length at the time. Unfortunately, I am not sure which is Calico and which is Lemon Drop since they were both very similar in their appearances at that time. I'm hoping you may be able to help with thay as well. One is black or a very dark brown with yellow-ish spots and white tips on it's dorsal and tail fin (I've been assuming this is Lemon Drop). The other (Possible Calico) is lighter overall (a green/yellow color) and the spots are a bit larger in comparison to it's body size. It also has a white tipped dorsal and tail fin.
So, on to my main concern, the Lemon-Drop has been chasing away the Calico, and occasionally will scare off the other fish. I realize that the Lemon-Drop will be territorial during feeding time and that's the only time I see him ward off the other fish (Glow-Tetras, Odessa Barbs, and Guppies).I usually feed all the fish at night before I go to bed and change the lighting to the Blue LED. I usually put 3 wafers for the Plecostomus' at once and in different locations of the tank (They are fed Omega One Veggie Rounds). At first I just fed them 2, but the Odessa Barbs seem to favor the wafers far more than the flakes. What worries me is that the Lemon-Drop will not only chase the Calico half-way around the tank but will sit, wait, and pursue the Calico even from far distances, almost as if he is hunting. Unfortunately, I've noticed the happening without it being feeding time. The Lemon-Drop could also just be eating a wafer, and the Calico is on the opposite side of the tank eating the other wafer, and the Lemon-Drop stops eating to chase the Calico away from any wafer in the tank and become possessive of it until the Calico sneaks to another wafer, and the process is repeated all over again. Also, I don't know if this means anything to you, but I've noticed that before the Lemon-Drop chases the Calico, he will stop moving, lower/flatten his dorsal and tail fin for a moment, and a moment later is when the aggression begins.
My tank is about 17/18 gallons, the Lemon-Drop is about 4 millimeters wider and longer than the Calico. They're both about a centimeter wide and 2 inches long. The only other fish in the tank are 4 Odessa Barbs, 2 guppies, and 4 Glow-fish Tetras. I have 3 plant decorations, 2 small-ish decorations, and one cave decoration. The only cause I can think of is a lack of hiding places. Do you think getting more plants and another cave would help the situation? And if not, do you recommend I do so anyways?
My apologies for typing up such a long question and explanation. I just wanted to make sure you had as much information on the situation as possible. I'd love to hear your opinion.
In both images you provided, the Pleco that is closest to the cave is the Lemon Drop, and the one closest to the camera is the Calico.
Unfortunately, male plecos are aggressive, especially toward other male plecos. There is usually just a chase as you described, they will rarely hurt one another. You could try adding more plants and another cave, or possibly even a much larger tank would solve the problem.
Other than that, I wouldn't worry about them too much, the Calico will get his food when he's hungry enough.
Hope this helps, good luck!