Oh gosh - there's nothing wrong with you, I swear! Dreams are symbolic, so my guess is that it actually doesn't have anything to do with animals at all... That said, if my interpretation doesn't ring true to you, please let me know and we can work on it together.
Also - I have a couple of questions, but I'll try to work them into the narrative here.
First off, I think that the animals represent something in your life that you're nurturing - like a goal, or project. Since the animals are small, my guess is that whatever you've been wanting to pursue isn't something huge (like a new career), but is something that you view as a 'hobby' or 'side project' - it's not as if you want to change your entire life, you'd just like to dedicate more time to whatever this is. In your dream, you were having difficulty keeping the animals alive, which seems to say that this goal you've always harbored is kind of slipping away. Perhaps you feel as though you're getting too old to do it, or you tell yourself it's "silly." But your unconscious mind is telling you otherwise. It's telling you that you need to nurture this goal more to keep it going.
However, I'm not sure about the context in which you found yourself - the environment. For instance, was the fish tank clean and sparkly and beautiful, or was it cracked and dingy and in need of repair? These details might give me a bit more to go on. Additionally, how did you feel in the dream (not after you woke up)? What were you doing to keep the animals alive?
Thanks - I look forward to hearing from you!
Alright - thank you! The reason I'd asked about the condition of the tank and your surroundings is because I'm guessing that those details correspond with your environment. So, in the fish tank dream, I'm guessing that you feel that your environment isn't exactly 'right' for nurturing your goal or project. You may also feel that others in your life are sabotaging your plans a bit (not necessarily on purpose - like your mother putting the wrong water in the tank). So, all in all, I'd say that you may be dreaming about dusting off some old ideas or pursuing a project, but you feel that you don't have the necessary support to do so. Thus, your stab at this goal keep failing (the animals 'dying'). This may be your unconscious's way of encouraging you to actively pursue whatever this is.
What are your thoughts?
Oh, that does make sense then. Your unconscious is just playing out that anxiety of trying to realize your goals with all the constraints. It makes more sense too in that your mother was in the dream. If you live with them, it probably feels like you're often "in the wrong water" when it comes to trying to get things done.
The good news is that you're far from giving up. Your dreams feature a struggle - which can be disturbing, I know - but you haven't succumbed, and aren't hopeless. On the contrary, since your dream self is working so hard to keep the animals alive, that tells me that you have a fair amount of drive left.
Keep at it, and once some progress is made, I think your dreams will change substantially. :)