Rainbow fish display tank setup guide

Before you buy a single piece of kit for your rainbowfish display tank, the most important concept to understand is the nitrogen cycle — your tank needs to establish a colony of beneficial bacteria before it can safely house fish, and skipping or rushing this step is the number one reason new tanks turn into fish graveyards. Once that's under control, rainbowfish are a fantastic choice for a showpiece setup, but they do have some specific water chemistry preferences worth planning around from the start. Are you starting completely from scratch, or do you have an existing tank to work with — and what size are you thinking, and which rainbowfish species are catching your eye?

Great choices — Boesemani and turquoise rainbows together make a stunning display, and they come from Lake Sentani and surrounding regions in New Guinea where the water is indeed soft and slightly acidic, pH around 6.5–7.5 and hardness below 150 ppm ideally. The good news is that both species are reasonably adaptable, and many fishkeepers in the UK successfully keep them in moderately hard tap water as long as it's stable and well-cycled. That said, if your tap water is very hard — say, above 300 ppm — you'll want to blend it with RO or softened water to bring it down. What's your tap water hardness if you know it, and have you tested it yet?

London tap water typically runs 250–320 ppm, which is on the upper edge for Boesemanis — workable but worth monitoring. The very first thing to buy is a water conditioner, and for your situation I'd specifically recommend Seachem Prime. It's not just a dechlorinator — it also detoxifies ammonia and nitrite for up to 48 hours, which is genuinely useful during the cycling phase when those compounds spike. For a 200-litre tank cycling from scratch, that protection buys you a real safety margin, especially since London water also contains chloramine rather than just chlorine, which standard dechlorinators handle less reliably. A 500ml bottle treats enormous volumes and lasts a long time. Beyond that, you'll want an API Master Test Kit to track your ammonia, nitrite, and nitrate through the cycle — there's no guessing your way through this, you need to see the numbers.

A fish-in cycle typically takes 4–8 weeks; a fishless cycle using ammonia can take the same but you're not risking livestock while it runs. The fastest legitimate shortcut is using bottled beneficial bacteria — Seachem Stability is solid — or better still, getting a handful of mature filter media from an established tank, which can cut weeks off the process. You'll know the cycle is complete when you dose ammonia, and within 24 hours you're reading zero ammonia, zero nitrite, and a measurable nitrate. On the water hardness front, once you've cycled and are ready to stock, I'd suggest picking up a cheap TDS meter and a bag of peat or some driftwood for the tank — both will gently buffer the pH down and soften the water naturally without dramatic swings, which rainbowfish hate more than hardness itself.

Exactly that order. Prime and the test kit before you even fill the tank, run your fishless cycle watching the numbers daily, and only add the Boesemanis and turquoise rainbows once you've seen that complete cycle reading. With a 200-litre tank you'll have room for a proper shoal — aim for six or more of each species, because rainbowfish genuinely colour up and display better in numbers. They're active, sociable fish and a large shoal in a well-planted tank is one of the best displays in the freshwater hobby. You're setting this up the right way.