Add some neon tetra and pound your heart out as you watch them swim around the tank. Fast-forward two months… the colors aren’t so hot anymore, and then bam! One of the fish dies belly-up overnight. What happened? Ammonia and nitrate is both zero. WTF?
The answer may be invisible. Even if your tap water looks clear, something else might be in it. You can fix this by making sure minerals in your water match biology of the creatures you are trying to support.
Why Water Minerals Are Important for Your Fish
What we’re talking about here is water hardness, or more specificly, the mineral makeup of the water in your tank. In other words, it is about how much dissolved stuff is in your water, mostly calcium and magnesium. These is the main minerals used to classify water hardness. Here’s how they break down: General hardness refers to those minerals or structural minerals. Carbonate hardness refer to the buffering capacity, or the ability to maintain pH stability.
Bottom line: don’t treat these as the same because treating them so will set you up for unexpected swings in levels, crashing your tank and killing off whole colonies overnight. Sounds crazy, I know, but it’s a very subtle distinction that means everything when trying to achieve long term stability.
Your local tap water will serve as your baseline against which you should of judge what’s realistic for you to keep without spending big bucks on equipment. For example, if you live in an area with soft water (Southeast Asia, parts of Scandinavia), then you’re at a built-in advantage for keeping some Amazonian species that thrive in low-mineral, acidic conditions. Fish like cardinal tetras or discus simply cannot handle the mineral load present in harder waters, they will experience osmotic stress and weakened immune systems over time.
On the other hand, African cichlids from the lakes of Tanganyika or Malawi needs alkaline conditions and high mineral levels to stay healthy in terms of their bones and color. Attempting to make that water soft for a soft-water fish is typicaly more trouble than it’s worth. When you adjust your water chemistry against the grain (forcing a square peg into a round hole), you’re likely in trouble.
For instance, you may add crushed coral to make the water harder for cichlids. However, the high carbonate level will lock up carbon dioxide, which stunts plant growth in your planted tank. Or perhaps you use rainwater to soften the water for your shrimps, not realizing that pure water has no buffering capacity and the pH will swing violently and unpredictably to unsafe levels before you know it’s even happening.
This is where shrimp keepers has the steepest learning curve as these invertebrates are much more sensitive than fish. Specifically, Caridina shrimp is highly sensitive to very soft water. They require a precise balance of minerals to molt successfuly. In contrast, Neocaridina species like cherry shrimp are quite forgiving and can tolerate moderate levels of hardness. A few degrees of General Hardness is often what separates success from complete colony failure.
There’s no guessing, you must measure it accurately (liquid test kit, not cheap dip strips which provides only rough estimates). Regardless of what you’re doing, make adjustments slowly and deliberatly. You can add more minerals, such as certain types of mineral salts or even limestone, to adjust hardness up. Go easy. Do so incrementally… Over several days.
Trying to decrease hardness? Usually this means using reverse osmosis filters then meticulously remineralizing the water with care in order to have exact control over the hardness levels. It’s a pain but once you understand why…well. You get the picture.
Make things stable. Make things comfortabley for your fish and let them feel like they are at home. To conclude. Aquarium keeping boils down to aligning things. If your water is fine, use fish/specifics that fit it. If not, spend money to change it drastically. Don’t try to maintain average conditions and expect everything to be happy with that.
Test your tap water every week, pay attention to what happens when seasons shift, and tweak accordingly. Because your livestock will tell you so much more then mere test results on paper will. Get the minerals correct and the rest happens automatically.
