Harlequins make excellent display fish for planted tanks and aquascapes because they add contrast to a tank as well as visual appeal. But, Harlequin rasboras, like neon tetras, prefer to swim in dense schools.
Harlequin shrimps are shaped slightly like a praying mantis with leaf-like appendages. This is a relatively small shrimp. A fully-grown Harlequin shrimp can reach up to ~5 cm (2 inches) in size, which can really make them stand out in smaller aquariums.
Your Harlequin Shrimp requires a 10-gallon or larger tank. They will spend their time among the rocks and coral. Their size, striking color pattern, and active nature ensure they stand out regardless of the tank size.

How Important is Tank Size for Goldfish? Whats the Minimum Tank Size?If the tank is too small, the goldfish will not have enough room to swim and explore. This can lead to boredom and health problems. Goldfish are very active fish and need a lot of space to stay healthy.
Does a small tank size inhibit goldfish growth? Learn all about goldfish tank size with this detailed ([year]) guide...

The best size tank for goldfish will depend on how many and the type of goldfish you intend to keep. There are over 300 species of goldfish, and they come in all shapes and sizes.
The perfect tank size for two or more common goldfish is 40 gallons, plus another 12 gallons for every extra fish 52 gallons for three common goldfish, for example. Equipment Needed to Set up a Goldfish Tank.

As we can see from the illustration, Small Tank Size For Goldfish And Harlequin Shrimp has many fascinating aspects to explore.
Planted Tanks for Goldfish. Fancy goldfish and swimbladder/buoyancy problems.Different tank sizes are often quoted for common or singletail goldfish, and fancy goldfish. Goldfish can be divided into two broad types; singletails (often referred to as commons) and fancy goldfish.