I'm still not so sure about that extension tube. It really seems that's when things get messy. Both the other two cap shots are pretty nice, actually. This bottom one (that looks more pink) is probably a tad bit oversharpened, but these aren't as bad as you're making them out to be.
Drop that ISO as low as it goes. Try shooting with an aperture setting around f/8 to f/10, or so.
But yeah... there seems to be a real loss once that extension tube comes on, and I don't know anything about them to be able to help you. For now, I'd leave it aside until you figured out the shots without it, then bring it back in to the picture (no pun intended )
Just giving you a hard time, sorry if it came across stronger than that.
I'm also running out of things to post, as I feel like I've shot about everything in my lil tank. This thread will be good for me, it will force me to be creative, and find new things in the tank.
And I have yet to get a good shot of my fourth fish, the 6-line wrasse.
Maybe I should check what I type, I edited my post. I just wanted to know If one will kill the other or just damage part of it, what is the best solution to preventing this, maybe just more distance apart I'm guessing would help. Would it be ok to just leave it alone & let one take over the other maybe?