You get 5 Aquabux a day so long as the fish are alive in your tank.
Any item or fish purchased is 'unlocked' to use as many times as you want once purchased or gifted to you.
So... say you only use the default tank, which is a maximum of 3 fish and 3 decorations. If you waited 10 days, you could use the 50 Aquabux you've obtained to buy a 50 AB fish, and put 3 of them in your tank if you empty the old fish out or started a new tank... think of the fishbowl items like Rewards for Home, once you have it, you can always use it.
I don't budlist-add on forums, and blank PSN requests get ignored!
Missing Rewards -over a year old, still never fixed! 3-4 months worth of items still MIA.