Fishdom 3: Special Edition
20 Achievements
200
25-30h
Good student
Gain enough Experience to reach Level 25
10
How to unlock the Good student achievement in Fishdom 3: Special Edition - Definitive Guide
Experience points are gained for finishing playing levels, making purchases to improve your tanks, cleaning the tanks and feeding your fish. I found that adding low cost fish to max out each tank helped since every time the fish were hungry, there were more to feed and give exp points. I also found that the tank level went up more with when I bought figures instead of plants (when spending the same amount of money.) Each trophy level that you get by upgrading the tank (for adding figures or plants,) increases the number of fish you can have in your tank. Hope this helps.
The only way to gain experience in this game is to purchase stuff from the shop. The fastest way to level up, in terms of XP received per coin spent, is by buying fish. However, since there is a finite number of fish your aquarium can hold and since you will need to spend your money on decorations to upgrade your tanks for the "Perfect aquarium" achievement, this is the most efficient way to level up while working on all achievements:
Right from the get-go, always spend your money on decorations for your tank. The "Perfect aquarium" achievement is a long term achievement that you'll need to work on constantly as you progress to level 25 and ultimately to level 48. The higher your level, the more money you get from completing levels, so you definitely don't want to stockpile money. That being said, there's no need to continually buy the cheapest decoration over and over again. What I would do is gauge how many of the most expensive decorations I'd need to reach the next level, save up money, and then buy them to level up. Any levels you play while you could have been a higher level are just a waste of some extra money you could be earning.
Refer to the "Perfect aquarium" achievement solution for how to properly manage your money for the bulk of the game. Once you fully upgrade five aquariums, there's no need to buy more decorations. Buy fish, since they get you more XP, and you should have lots of capacity for fish in your tanks now. You should make it a point to buy each type of fish, since you'll need to anyway for the "Ark" achievement. Also save up and buy more aquariums until you have ten for the "Great aquarist" achievement. Aquariums give you the same XP ratio as fish, so it's worth buying those when they unlock.
Once you've upgraded five aquariums fully, bought ten aquariums total, and bought each available fish, you can actually then sell all your fish and all your decorations to make some money back. You can then use that money to buy more fish to get more experience, and then sell them and repeat until you're out of money. This will give you a sizeable XP jump at this point. You can then continue to play levels and spend money on fish to level up as quick as possible.