I use aquarium note, I paid for it but I believe there is a free version. I can set reminders, have multiple tanks listed, include logs like when I last did a water change and can keep a record of my parameters. It also has a live stock section where you can keep track of what you have. If you enter the date you acquired any live stock it will keep track of how long you've had if for. Same for equipment and your tank itself.
It's not overly fancy but it does what I need.
*Edit for spelling, I swear autocorrect has it out for me.
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