Harlequins are hardier than many sources suggest, if you take care that they get a chance to adjust after moving them. In my experience they will do fine in neutral pH if you are not aiming to breed them. They add a lot of color to a community tank, while not looking artificial and being small, and they will not make a huge impact on the bioload of your tank. It's not often you find a species as attractive, active and non-agressive as this one. I have 6 in my 40 liter community tank which is working fine, but another way of keeping them is in a large shoal of 30 or more in a larger tank devoted especially or built to feature this species. Lots of bright green, leafy plants and a large piece of driftwood will make a tank with a large school of harlequins a rare sight without it having to be a lot of work. The more fish you have, the more they will school. The whole group will swim back and forth in unison.
I have had an excellent experience with this fish. They are very hardy and in my opinion can adapt to a wide range of conditions. I have mine in a pH of 7.4 and they breed for me every morning in the rays of sunlight that fall on the tank before the lights turn on. The fish have almost doubled in size in the month or so that I have had them. While breeding the males get pretty agitated and enjoy having space to swim up and down beside each other in their little squabbles. Make sure that you have at least two females to every male, or the males will never stop fighting. These fish like to lay their eggs on the undersides of broad leaved plants. I use amazon swords, anubias, and java fern. These fish will devour their own eggs with relish, so make sure you keep an eye on them while they're spawning. I actually have one fat female that just follows around the breeding pairs sucking up the eggs like a little vaccuum. When I eventually decide to raise the fry I will have to remove her from the tank.
These rasboras have been my favourite small fish for years. I've got them in two different tanks. They shoal well together. Don't let the tank temperature get over 27°C as it can be fatal for the rasbora. Feed them live foods such as brine often and their colours will not be beaten.
My Harley Gang are quite bold little fish but they really need each other's company. When the tank is disturbed (by me cleaning it or adding fish), they shoal together protectively. They are definetly more interesting in a shoal; one alone would probably fade away and hide. Mine love racing along the tank, and swimming down into the bubbles of the air curtain! Hearty eaters, great little fish!
I have had 2 harlequin rasboras for a year now and I have to admit that they are very easy to maintain, as well as very peaceful. I keep them together with 6 neons, 2 white cloud mountain minnows, and 2 cherry barbs - total of 12 fish in a 115 L tank. The pH of my water is around 7.3 and they're all doing just fine. I know that the pH level for the fish I have should be soft and acidic, or at least neutral, however most of the fish we get in pet stores have been bred for generations and are used to tolerate wide ranges of pH. In fact, maintaining a stable pH is more important than constantly trying to change it, since rapid pH changes can have disastrous effects on fish. Going back to harlequin rasboras - not only are they relatively easy to maintain and very peaceful, they're also beautiful and will look great in your tank. I would recommend this fish to anyone!
In my experience with the Harlequin Rasbora it has been quite an awesome fish to keep. I have kept the Harlequin Rasbora in my 40 L planted tank for 1/2 year now with 2 Zebra Danios, 1 Amano Shrimp and 1 Yo Yo Loach. I have never had any problems with my Harlequin Rasboras. They are a very peaceful and relaxing fish to watch as they school in a fish tank. They favor the middle of my tank and are usually the first fish you look at when you see my tank. I suggest anyone to get the Harlequin Rasboras in their tank if they don't have any aggressive fish to bully them.