I’ve had water in my big tank since October 13th. My family and friends are always shocked that I don’t have any fish in it yet. There’s a reason! (Well, several reasons, but one main reason.) I thought I’d elaborate for the tank update this week. For those of you that have any experience in the hobby, this is going to be old news. For those not familiar, this is the keystone to basic, happy fish keeping.
Aquariums are mostly closed systems. The flow of fresh water into the tank is periodic — i.e., happening only when we humans take out old water and put in fresh clean water. In between, waste products from living organisms, decay, and changes in water chemistry due to things like driftwood all accumulate in the tank. It won’t be a surprise to anyone that swimming around in their own waste is bad for fish. This is one of the central problems after creating an acceptable habitat in the first place.
Fish excrete ammonia as waste. Their stool and other decaying things in tanks also release ammonia. Ammonia is very toxic to fish. It burns their skin and gills. If the ammonia gets too high, fish can be killed. Other organisms, like my freshwater shrimp, can’t tolerate ammonia at all and will die if it’s present. If the ammonia went untouched, every fish tank would poison itself and kill the non-plant inhabitants.
Thankfully, bacteria come to the rescue! There are naturally occurring bacteria that will convert the ammonia into a less toxic form called Nitrite. Then, different bacteria will convert the nitrite to nitrate, which is the least toxic form. Then, when we perform a water change, the nitrates are removed from the tank. Fresh, nitrate- and ammonia-free water is put into the tank. We wait for the bacterial cycle to raise the nitrate level to a point that we once again need to change the water. This beneficial process is called “Cycling.” It can take a few weeks to a few months to happen.
Let me restate that. Growing the right kind of bacteria requires ammonia to be present in the tank. Even then, it can take a few weeks to a few months for this to happen. The way we know that the cycle has occurred is to test for nitrates in the water. When nitrates are present, there is a population of bacteria converting ammonia to nitrite and then to nitrate. That’s when we know it’s a safe tank for fish or other organisms. There are two ways to go about getting your tank to cycle. They’re called “Fish In” or “Fishless” cycling.
Fish-in cycling requires the aquarium to be stocked with fish that are very hardy and can withstand some ammonia and nitrite in the water. Some of these fish favor water with a little bit of salt in it (brackish), which helps decrease the ammonia/nitrite/nitrate toxicity. Fish-in cycling is most commonly what people do because they’re interested in having fish right away.
The other method is one in which the human acts as the source of ammonia for the tank. Fishless cycling requires that ammonia (pure, with no other chemicals) is added to the tank to encourage the bacterial populations to grow. The amount of ammonia is calculated to maintain a certain level in the water, which feeds the bacteria.
When the cycle is running well, we can test for nitrates. When nitrates are present, the cycle is complete, and living things can be added safely to the tank.
Testing is best done with a liquid chemical test kit. There’s one that’s sort of the gold standard, which is what I have. It’s fairly easy to perform these tests. A specific amount of tank water is put in a test tube. Chemicals are added to that water sample in a specific amount and order. The readings are made by comparing the color of the water in the test tubes to a chart.
In the photos below, you can see the test kit’s chemicals and my two water samples. I’m testing for ammonia and nitrates. This ‘first and last’ testing lets me know that the cycle is complete, but also that I’m feeding the bacteria well enough. Remember, ammonia is needed to create the cycle!
When it’s time to read the test, I compare colors in the tubes to the reference chart. For me, the ammonia is at or less than 0.25 parts per million (ppm). The nitrates are about 30 or so, which is higher than I like to have them. I’m planning to do a big water change tomorrow to get rid of some of the nitrates.
With the knowledge that my tank is producing nitrates, I can comfortably add plants and gradually add fish to stock the tank. The only catch is that I need to order the big, bright LED lights that will help my plants grow. The wimpy fluorescent bulbs I have now just don’t have the strength to grow plants well.
There are a couple of good tricks to cycle a tank faster. You can take things from an already established tank and use them to ‘seed’ a new filter or tank. It’s sort of like transplanting a healthy ecosystem into a brand new one. The other way is to buy the beneficial bacteria in a bottle. Several companies sell these tank ‘probiotics.’ I’ve used them in the big tank to help with a jump-start. There is debate about whether the specific species of bacteria in these quick start liquids will stay alive in a big enough population in the tank for long periods of time. Most of the quick start manufacturers advise “boostering” the tank monthly with their product. I find that fairly off-putting given that they advertise as being a ‘natural bacteria source.’
I personally selected a fishless cycle for my tank. I’ve been adding ammonia to get the bacteria to product nitrate. I’ve also poured in a bunch of duckweed, which is usually a “pest’ plant that people run away from as if it’s the herpes of the aquarium hobby world. The plants, however, will use nitrates to grow. This helps reduce the nitrates in the tank water and lets me change the water less often. It’s also better for the fish. Plants provide hiding places and beneficial chemistry.
In the test above, the ammonia is under the 4ppm that I prefer to have, so I’ll be adding some ammonia tomorrow after I change the water to lower the nitrates. Once I have the lights, I’ll be buying plants and then fish to stock up the tank.
So, the short answer is that it takes a long time to get a tank ready to house fish in a healthy, non-toxic environment. It’s all about the bacteria!