With all due respect, I disagree.
Animals on this planet are to be taken care of; it doesn't give us any right to put them into bad stituations with the idea that God will come to their aid because we screwed things up. God gave us free will, which some use to abuse. This many fish in this tank was a choice, and they are all dead from that choice. That is hard to hear, but it is true, whatever the causes that led to it, and we need to learn from it. Many animals die because they were not taken care of by those who were entrusted with their care, day in, day out (watch Animal cop shows on animal planet!!). They die from being starved, abused, or living in overcrowded conditions...or bad water. These are physical realities; we will never learn if God bails our sorry selves out of everything.
It is God's challenge to us to learn to care for this creation, and use them for our benefit, so long as we do so with compassion. He works through others, by giving them talents to learn and write books for others to learn from, just as he works through the hands of skilled doctors. It is for us to learn to take care of creation, not for him to bail us out every time we choose to ignore what has been learned.
I am glad that you have learned from this experience, and grown from it. That is God's message, IMO. Take care of what has been entrusted to you. Give them the best possible life now that they are in human care. Find the right food. Get the right tank or the right fish for the tank. Find a better store. Get some books. Don't overcrowd the fish. And you know what? Some fish will still die, but you learned to do the best you could for them, and that is all anyone asks.