Nathan Hill’s Neon tetra biotope — a step by step guide

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None of our tank set-ups has ever divided opinion like this one. But whether you love or hate this biotope, it was one of the most rewarding in terms of fish behaviour!

WORDS: NATHAN HILL

Chuck it in a tank with a load of ****. Hey presto! Biotope!” That was one less than glowing appraisal of the wood in my layout when I showed it off online. Get a tank, the theory goes, stick in some choice wood and a load of gunk, and you have a biotope. If only it had been that easy.

In reality, this Neon tetra biotope has been an arduous and long-winded project — perhaps my most protracted to date. It’s also up there as the most rewarding.

Biotope aquaria are a law unto themselves — set-ups that aim to reproduce a specific slice of nature. I’d love to say who first invented the concept, but I can’t. At some stage within the hobby, it just made sense to recreate the wilderness to a faithful degree.

Biotopes can be loose or accurate. A loose biotope tank will go as far as melding fish and plants from one specific country. The species it contains might inhabit a range of different terrains, never crossing paths in the wild, but they will share a far-reaching geographic bond. This kind of set-up has a mild ‘zoo’ feel about it, with its mixed curiosities.

An accurate biotope seeks authenticity down to the tiniest detail. It may incorporate seasonal changes, and wet and dry periods. Hardcore ’topers will seek out images of specific streams and pools, finding which fish, plants, sand, rocks and branches are there. I’ve known some to actually visit the exact regions they want to copy, importing back fish they collected themselves.

I wanted my own biotope to be simpler — to encompass all that I desired from nature, while being something that anyone with a tank could muster. I wanted authenticity, but only as much as I could recreate without straying too far from the comfort of home.

The internet has spectacular resources for inspiration — if you’ve no computer at home, you can still get online via your local library. Get on Youtube or Vimeo, and follow some ichthyologists out in the field. My own preference is Ivan Mikolji, who lashes cameras to himself as he dives about in Venezuelan waters. The footage he captures is little short of revelatory.

One of Ivan’s videos was the precursor to this set up. A scant five seconds of footage, to be exact. If you watch it, then you’ll see from 2:17 to 2:22 the exact few seconds that sparked it all. That vision, right there, was what I wanted to reproduce.

So now I had a plan. I had my inspiration, and I set aside some time to make it all happen. All I had to do now was put it together, but what a nightmare that would soon become…

Sourcing the essentials

I chose the humble Neon tetra, Paracheirodon innesi, because I’d never seen it in a focussed, species-only biotope before. Despite being one of the commonest species on sale, most are destined for either community tanks or aquascapes. A handful may end up in mixed, loose biotopes around the country, tossed in with dwarf cichlids, or a plethora of other tetras.

I wanted to create a South American, algae filled, leaf-littered, flooded forest pool. So I asked a handful of explorers who had been there what they were like.

Responses were varied. Some said sand and silt as a substrate. Others said dark, mulchy and muddy stream beds, with a deep bed of leaves. In some areas there were plants. In others, just thick gardens of algae. There was or wasn’t floating vegetation. One theme that did recur was that although leaflitter was often prevalent, water wasn’t always stained black. Several reports cited clear water, albeit a little turbid.

Wild Neons seem pretty unfussed about water depth, so instead of a tall tank I concentrated on providing a decent footprint, so that a generous leaf litter carpet was doable. As I had an Evolution Aqua Aquascaper tank sat idly awaiting a project, it was drafted in for the job. The dimensions of the tank — 60 x 50 x 30cm in depth — would allow the fish to spread out in all directions, as opposed to the restrictions of a narrower, almost twodimensional aquarium.

I wanted plenty of naturally occurring life in amongst the substrate, so catfish were out. I wanted something dark, into which a cornucopia of invertebrates could delve. I settled on a coarse planting substrate, in this case Prodibio’s AquaGrowth Soil. On paper, the grains claim to be assorted from 1–3mm in diameter, but really they’re all closer to 3mm — 9 l of substrate was adequate for the job, and gave me a labyrinth of tiny nooks and crannies that microorganisms would thrive in.

Hardscape proved to be my greatest sticking point. I’m in the privileged position of having vast stores of aquarium decor, but absolutely nothing would work. Redmoor root looked like Redmoor root, completely out of scale with the video clip I was basing my project on. Bogwood was excessively chunky and had no form — it looked nothing like the wood of a flooded forest. Mopani wood screamed out, too bright against the black substrate. After a couple of days, I hit a creative wall.

Epiphany moment

I went for a walk, and epiphany struck. As I strolled, my pathway became a dirt track, which led to the tree-heavy fringes of my estate, where Beech, Birch, Sycamore and Alder trees run riot. There in front of me, were mixed fallen branches, of exactly the right texture and scale. After some light scouring, I’d attracted the attention of a local woman in her garden, just where I was sizing up an attractive Sycamore.

After a brief chat, she mentioned she had some fallen branches from the trees in her garden. One branch of about 1.5m long, dried and on the verge of rotting was exactly what I needed. With a quick swing over a fence, I was set, and on the right side of the law, too. Since 2008, when the right to forage for firewood (a right given under the Magna Carter) was overturned, it became illegal to collect wood for domestic use on common land.

Next up, I needed leaf litter. Thankfully, I had tonnes of bags from Tannin Aquatics. What I was sat on wasn’t specifically South American, but that didn’t matter. As everything would be decomposing by the time the fish went in, anything identifiable at that stage would be a drawback!

I have external canister filters ranging from an ADA Superjet to a Fluval FX4, and everything in between, but all of these would churn up my wonderful detritus — for this job I needed something smaller, so despite owning more filters than most wholesalers, I went out and bought a Tetra IN800 internal canister. The reasons were twofold. Firstly, the flow is easily controlled with a frontal dial. I can tweak it in real time. Secondly, when removing the filter media chamber, the design doesn’t backflush and drop waste out as I’m trying to lift it from the tank — a real bane with some internal canisters.

To heat, a simple Fluval 200W heaterstat would do the job. In the event, I had to commit a heaterstat sin and position it bolt upright. I’ve done this a few times with Fluval heaters and on the whole they’ve held out well, though mine did make some curious noises while it was running. Lighting the tank fell to two Fluval Ecobright LEDs. At 7500K, they gave the white light I wanted to bring out colours and wood textures, but they’d also have enough coverage to promote the floating plants I envisaged on the surface. In the event, they did a little too well in that role. With the key ingredients sourced, I could finally get the tank together...

How it came together

Before adding any equipment, I had a few dry runs with the decor, so I would be certain I could make it work. My branch was snapped into segments and arranged before I upended all my dry leaf litter and seed pods over it. The effect was, if I might be so bold, striking on the first attempt. I photographed it and stripped it back down before arranging it properly.

1. I wanted leaf litter but not blackwater, so I had to get as much extracting done as possible before the leaves went in. I started off by steaming my pods, wood curls, and Carambola lixo leaves, while boiling up my Magnolia, Guava and Catappa leaves. After half an hour of that, the water was drained away (I used this tannin extract to fill a one-litre bottle, for use on later blackwater tanks). I replaced the water with fresh, boiling water, and the steamed elements joined the core leaves in the saucepan. Boiling water was drained off and replaced every ten minutes for the next hour, until the water appeared clear.

2. To secure my backing sheet to the rear pane of glass, I use sticky ‘dots’ which can be bought in packs from stationery suppliers. The dots are discrete compared to large squares of double sided tape, and have the benefit of remaining sticky even when I pull the sheet away and reattach it. The substrate is added and sculpted so that it lifts towards the middle, which will add a little height to the decor in the centre.

3. The core, large wood pieces are added. I’ve taken the rare and ill-advised move of leaving my bark on, which presents two problems; the wood will now be more buoyant than usual, and it’s important to note that some barks leach toxins. In my case, I know there will be so many water changes over the coming weeks that I’ll dilute anything that does end up in the water. I position the filter in the rear corner at what I expect my eventual water level to be.

4. The remaining large wood pieces are added, though slightly different to my initial dry run as I find a way to position them to add extra lift. Smaller twigs are added for effect over the top, arranged in such a way that they stretch from left to right, drawing the eye away from the filter. Happy that they do this effectively, I also position the heater next to the filter.

5. In anticipation of the wood floating, multiple rocks are used at strategic points to help pin them down in position. At this point, I have no idea how buoyant the wood is, or how long it will take before it actually sinks.

6. With the wood now in its final position, I add one of two plants I’ll be using — Hairgrass, Eleocharis acicularis. The plan is to not interfere with the Hairgrass at all and let it run rampant, sprouting up wherever it wants to. Hairgrass has been deliberately chosen as it is notorious for trapping algae and sediment, which in turn will bring the exact ‘natural growth’ look I’m after.

7. Water is added — and within seconds I find out just how buoyant that wood really is! It lifts the rocks like a raft, and uproots nearly everything. After a tussle, heavier, bulkier rocks are brought in so that there are now more rocks than there is wood being held down. Then the Hairgrass is replanted.

8. The leaf litter is unceremoniously dispersed by dropping it over clearer areas of the tank. The plants will have to fight their way through it, but at this level, I want to avoid any leaves that look contrived. Now I can fill the tank to the top, fire everything up, sit back and wait — and as you’ll discover over the page, this is where the trouble starts...

Turning black

A few problems arose early on. Within days, the tank started to cloud over, but not the usual white clouding. My tank was turning black, a result of the depth of the leaves, the tiny organic particles that came in with the leaves, and the lack of circulation through it all.

After a large water change, I left the tank for a few days to attend an event, and on my return it was jet black. Not blackwater with tannins black, but black from a complete organic breakdown. The water could be better described as soot, and the smell coming form it was worse than any drained bog. The whole room reeked of rotting. The filter was clogged to capacity with sedimentary debris. More water changes took place, on a daily basis, but still the tank blackened again. Stirring the leaf litter released bubbles of foul smelling gas.

At this point, it must have been the mosttoxic tank in the UK. Ammonia test results were simply off the scale, and nitrite was doing its best to follow suit.

Blackness and foul smells became an almost constant issue, and the filter was continuously straining. But still, I persevered, refusing to strip it down entirely and quit.

I initially used Seachem Stability daily,later changed to Microbelift Nite Out 2, but I was asking a lot of it to start with. In an attempt to soak out some of the relentless ammonia, I added a handful of Salvinia, a nitrogen-hungry floating plant.

Next, mould started to appear, creeping out from the substrate and over my branches — the white, furry coating contrasted well with the black dust smothering everything. I let it run its course, gobbling up organics as and where it found them.

Eventually I conceded an air pump and airstone. I worried that the anoxic conditions were delaying development, and the filter was still clogging too frequently to provide reliable circulation. Initially, it caused an increase in turbidity, but this subsided within two days, after which the tank took on a whole new feel.

After around six weeks, the first life started appearing. Tiny planaria (small, pointy-headed flatworms) slithered over the glass. At the deeper parts of the substrate, long, threadlike worms burrowed.

Then the moment of reckoning. Some eight weeks in, there was a copepod explosion. Ostracods starting emerging in their hundreds, while tiny Cyclops-like beasts skittered about. The water turned crystal clear, instantly. Ammonia and nitrite became undetectable. Just like that, my tank had established. By now the Salvinia had formed into a thick, floating meadow — I removed 85% of it, and there was still too much.

I took out the rocks, only to find one piece of wood was still buoyant. Conceding defeat, I lifted it from the tank, calmly carried it downstairs, and hurled it into the garden for the woodlice to graze on.

My tank was now ready for fish. Everything I had hoped for in my initial vision had come to pass. Crumbling wood, dust and slurry, and a sea of life was at last together in a package that didn’t smell like a sewage outlet.

In go the Neons

When the Neons were added — 20 in total — it took just seconds for something feral to reawaken in them. Leaving the bag, they took stock of their surroundings, and set to task getting a ‘feel’ for the layout. In a darkened room with no tank lights running, I left them to it.

In the evening when the lights went on, there was a curious dynamic among them. Though they were in a loose shoal, there was a distinction between the lower-dwelling females, hovering just a couple of inches from the base, and the more adventurous, leaner males who would demonstrate to each other when they came close, with sudden chases and ‘shooing’.

The females would move in pairs or trios, exploring patches of substrate systematically, moving as one until a male would barrel in to them, scattering them again.

The real excitement came as I started to work the lights down for the night. Given the controllability of the EcoBright LEDs, I reduced the illumination slowly during the later part of the evening, noting that as I did so, the Neons — male and female — sunk down lower and lower into the tank, until the lighting was maybe one-third of its original intensity.

At this level, several of the Neons did something I’d never seen from them before. Hunkering down individually, and concealed within the leaf litter, they became stationary, but highly alert, with their eyes flicking around in what limited range they have.

They’d stay perfectly still — that is, until a copepod or ostracod would bumble past, at which point the Neon would shoot from its mooring, grab the tiny morsel, and retreat back to exactly the same position it had been in before, and resume its waiting. I watched several Neons doing this over and over, behaving like tiny Pike ambushing their miniscule prey.

As the lights dipped to their lowest settings, the fish started to club together again, forming a substrate hugging loose shoal.

For me, the ‘ambush hunting’ was the single greatest reward to the tank. Neons and I have a long history — they were one of the first fish I kept in a tropical community. I’ve sold thousands over the years, and witnessed them in hundreds of aquaria. But not once in my life have I had that momentary glimpse into the secret life of the world’s most popular tetra.

I strongly suggest you try something similar with your own favourite fish. Make it a home from home. Mature your tank, introduce your fish, and watch it closely. I’ll wager now that you’ll see something unique.

And besides, it’s easy. All you need is some authentic decor. Remember: “Chuck it in a tank with a load of ****. Hey presto! Biotope!”

You might want to open a window for a while if you do it, though...