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Fishy, fishy, fishy, fish

Previously, on ‘A Bug’s Life’, I wrote an update on my latest hobby.

Now, in that, I alluded to the need to ‘cycle’ the tank, because it’s brand new and it’s much better to have this going before I put live fish in it.

So, what is this ‘cycling’ I speak of?


Well, it’s not about riding a bike, that’s for sure. Also a fun hobby, but less aquatic in nature.

Turns out, the best way to remove any toxic fish waste from a fish tank, is to rely on microbes.

Fish waste is typically made up of ammonia or ammonium (depending on whether the water is acidic or alkaline), and over time, these compounds can build up in the tank, making it hazardous for living things. I guess it’s the downside of a closed system like a fish tank- the waste just stays.

A filtration system is a useful addition to a fish tank for this reason. It helps to ‘filter’ these compounds and remove them from the water, allowing the fish to live more comfortably.

Live plants can also mop up these compounds and use them as nutrient sources. It’s why a lot of compounds found in fish waste is also in fertilizer. The waste from the fish is food for the plants.

But the best helper in removing toxic nitrogen compounds from a fish tank are microbes.

They can help convert ammonia/ammonium into nitrites, and eventually, nitrates. These latter products are more easily taken up by plants.

Having aquatic plants that mop up these nitrogen compounds means that the plants will grow faster, and will therefore respire more- releasing oxygen into the water.

This oxygen can then be breathed in by the fish, which then allow the fish to grow and poop, releasing more nitrogen compounds into the water, which the plants, filter, and microbes break down…

And thus, a cycle is established.

Microbes are by far the most efficient at breaking down ammonia/um, so it’s really important to make sure that there’s a good population of them established in the tank, before you add a thing (i.e. fish) that will create more nitrogen waste.

These microbes also take up residence inside your filter, so the whole system gets a boost at waste removal. They also compete with algae for nutrients, so they can keep the gunk at bay as well.

Now, that isn’t to say you can’t add fish straight up, in a new tank, and just hope that the microbes will establish alongside the fish. It’s just a wee bit cruel if you think about it from a fish health’s perspective. You could potentially shorten its lifespan by exposing it to more toxic compounds than necessary. Newly bought fish are going to be stressed from the change in environment anyway, so you might also increase the likelihood of them getting sick.

So, thinking of the fish’s welfare, I set up my tank, and waited…

…and waited…

And nothing happened.

I bought a water testing kit so that I could monitor the pH, ammonia/um, nitrite, and nitrate levels. I checked every few days, but sometimes I’d go insane and check every day (REFRESH).

I started spiking the water with fish food every day, to introduce nitrogen compounds into the water. I added microbes to the tank (you can buy bottles of microbes from the pet store), checked the water, tended the plants, changed 25% of the tank water every week or two… then left it for a bit to see if a lack of water change would cause a spike in nitrogen…

Nothing changed.

The levels of ammonia remained low (<0.25 ppm) and there was no detectable nitrites or nitrates (constant 0 ppm).

Eventually I started to suspect that the added nitrogen from the fish food was getting mopped up by my fast growing plants, because they were going gangbusters. I’ve had to prune them back significantly because they were starting to take over the tank.

So, I trundled over to the pet store to make my case, and they agreed that if my vigilant monitoring didn’t see any spike in toxic nitrogen compounds, it might just mean that the system is ready for fish. I politely declined the basic flow chart diagram depicting microbial conversion of ammonia/um -> nitrite -> nitrate, on the grounds that I understood the core concept enough to get by… because bacterial metabolism was my Ph. D topic. The store person and I had a good laugh about how my life just revolves around microbes… but I guess they control all of our lives. 👀

Anyway, long story short- this is Miele, our hoovering, sucking catfish.

I’m hoping it’ll settle in, but at the moment, every time I see it swimming, I get concerned it’s trying to escape.

They’re supposed to be quite active, though, so I hope it’s just exploring its new home.

I’ll keep doing frequent water testing to make sure the tank is all good. It’s not like we have anything else to do while the state is in stage four lockdown for five days. 😂 It’s perfect timing, really.

Here’s hoping I don’t accidentally kill it…

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A Ph. D graduate in Microbiology, residing in Victoria, Australia. Currently working in multiple locations but still in the STEM field. 👀 🦠 🧫 🧬

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