White balance can definitely be tough. What I normally do is take a white object, like the white lid of one of your water buckets, or my preferred is a white cutting board I have. They also sell waterproof white balance cards you can use. Actually place the object in the tank, angled 45-60 degrees parallel to the lights and take a picture. You can then use this for a manual white balance setting (which I've honestly had mixed luck with) or my preference is to shoot in raw and then use this picture to get a good baseline for your white balance. From what I've found, it will usually get you close, but not quite where you want to be. I don't know if it's because the lighting for our tanks is just so much bluer than anything the camera designers had in mind and the white balance just can't always get it quite right, or if our eyes just do a little bit of their own adjusting, and what's in reality a correct white balance still doesn't look correct to us. In other words, an accurate white balance isn't always the "correct" white balance. Go take a picture of a sunset sometime with a good manual white balance. It just won't look right at all.
So, that's why I shoot in raw. You can manually adjust the white balance so it looks like what you actually see. Reality can be highly overrated.
As for your pictures themselves, they're pretty good, but decide what's really important in your photo and use aperture/depth of field to control what stands out in your photo. Otherwise, with everything we put in our tanks, it's going to look like a big, jumbled mess most of the time. For a full tank shot, having plenty of depth of field is a good thing, because you'll often want everything in focuse. For individual fish or corals, you usually want to limit your depth of field to that object, or perhaps just a portion of that object. Still, don't ignore your backgrounds. Although they'll be blurred, they are still a part of your photo. That can be a little tougher with fish who honestly make terrible models. They just don't listen to your instructions.
Here's an example of what I'm talking about. Although I knew I was going to have a cluttered background here, I limited my depth of field to give me something less distracting. It's also a good lesson on watching out for glare (look closely at the bottom right corner):
