Do not copy aquariums. Copy criteria. Start with your water.
Before setting up an aquarium, you do not need to become a chemist. You need to know what water you are starting with. That first reading prevents many mistakes: incompatible fish, plants that never settle, poorly chosen substrates, routines copied from another country, and water changes that do not solve the actual problem.
MACI does not ask for perfect water. It asks you not to build blindly.
Your Starting Water
Your starting water is the real point from which your aquarium begins. It is not an opinion, an internet average, or another aquarist’s water. It is the water entering your home and going into your tank.
Public supply, private well, storage tank, cistern, bottled water, RO water, or a mix.
Chlorine, chloramine, home filters, softeners, storage, or local treatment.
pH, KH, GH, and TDS/conductivity to read hardness and stability.
Nitrate, phosphate, smell, sediment, and seasonal variation if present.
Quick Path: What to Do Depending on Your Water
Use this table as a first decision tool. It does not replace testing, but it stops you from starting with a copied routine.
| Your case | First thing to do | Main risk |
|---|---|---|
| Normal tap water | Use conditioner and test pH, KH, and GH. | Copying routines without knowing hardness. |
| Water with chloramine | Use a conditioner that neutralizes chloramine. | Thinking that letting water sit is enough. |
| Private well water | Test pH, KH, GH, TDS/conductivity, and nitrate. | Nitrate, metals, extreme hardness, or variability. |
| Very hard water | Choose compatible fish and plants. | Forcing soft-water aquariums. |
| Very soft water | Watch KH and pH stability. | Low buffering capacity and instability. |
| Water with nitrate or phosphate | Test source water before blaming the aquarium. | Adding new load with every water change. |
| Storage tank or cistern water | Check consistency, smell, sediment, and treatment. | Variation, accumulation, or external contamination. |
| Bottled or low-mineral water | Check mineral content and stability. | Using water that is too poor without remineralizing when needed. |
Do Not Do This
A photo shows the result, not the source water, load, or maturity behind it.
Compatibility begins with water, not with the display tank.
Water can be safe to drink and still condition an aquarium.
Very poor water can also create problems if it is not stabilized.
1. Tap Water Is Not Neutral
Tap water can be drinkable, safe for people, and fully legal. That does not mean it is neutral for an aquarium.
An aquarium is not a glass of water. Fish, bacteria, plants, snails, shrimp, biofilm, microfauna, and roots live inside that water continuously. That is why hardness, KH, GH, pH, conductivity, chlorine, chloramine, nitrate, phosphate, metals, pipes, storage tanks, and seasonal changes matter.
This does not mean your water is bad. It means it is the first material of the aquarium.
2. Chlorine and Chloramine: Do Not Guess
Many water supplies use disinfectants to keep water safe until it reaches the tap. In an aquarium, those disinfectants must be neutralized before the water is added.
Free chlorine can dissipate more easily. Chloramine is more persistent. If your water contains chloramine, letting it sit is not a reliable solution: you need a conditioner that neutralizes chloramine.
There is no need to panic. There is a need not to assume. Check your local water report, ask your water provider, or use a suitable test.
3. Spain and Europe: Regulated Water, Not Identical Water
In Spain and the European Union, drinking water is regulated and monitored. That is good news. But for aquarium keeping, drinkable does not mean identical everywhere.
An aquarium in Galicia does not necessarily start from the same place as one in Mallorca, Madrid, Teruel, Valencia, the Canary Islands, or a rural area with well water. Hardness, KH, pH, conductivity, nitrate, and supply stability may all change.
The correct reading is not to fear tap water. The correct reading is this: your water can be perfectly drinkable and still condition what kind of aquarium makes sense.
4. United States: Chloramines and Private Wells
The United States deserves special attention for two reasons: the use of chloramines and the number of homes that rely on private wells.
The EPA explains that chloramines are commonly formed when ammonia is added to chlorine, and that they are used because they provide longer-lasting disinfection through the distribution system. For aquariums, the consequence is direct: if your water contains chloramine, your conditioner must cover chloramine, not only chlorine.
With private wells, the MACI rule is simple: test before designing. Well water can be excellent, but it can also contain nitrate, metals, extreme hardness, or seasonal variation.
5. United Kingdom, Australia, and Other Countries With Regulated Supplies
In countries with regulated water networks, the common mistake is trusting one word too much: drinkable.
Drinkable means suitable for human consumption under sanitary standards. It does not automatically mean ready for fish, shrimp, aquarium plants, or aquarium bacteria.
The practical reading is the same: check your local water report, confirm whether chlorine or chloramine is used, use a compatible conditioner, and test hardness, KH, GH, and nitrate.
6. Latin America: Do Not Generalize by Country
Talking about “Latin America” as if it had one type of water would be false.
Within the same region there may be large cities with treated public water, neighborhoods with variable infrastructure, homes with storage tanks, rural areas with wells, cisterns, bottled water, local collection systems, or mixed sources. The MACI conclusion is not distrust: it is to design from the real water entering your home.
7. Private Wells, Storage Tanks, and Cisterns
Private well water, storage tank water, or cistern water can work in aquariums, but it should not be used blindly. It may vary with rain, drought, infiltration, nearby agriculture, pipes, storage conditions, or tank maintenance.
Before setting up with this kind of water, test at least fresh pH, pH after 24 hours, KH, GH, TDS/conductivity, nitrate, and, if possible, phosphate. If there is smell, color, sediment, or suspicion of metals, do not ignore it.
What Type of Aquarium Makes More Sense Depending on Your Water
Aquariums with hardness-tolerant species, resilient plants, and less fighting against pH.
Aquariums where KH, stability, and mineralization should be watched before adding too much load.
Aquariums with functional plant mass, measured load, and water changes that are planned, not automatic.
Systems with margin: volume, plants, filtration, observation, and fewer abrupt changes.
8. The Mistake of Copying Aquariums Without Copying the Water
Online, we see finished aquariums: green plants, healthy fish, clear water, specific substrates, specific filters, and routines that seem to work. What we do not see is the source water.
Two aquariums that look almost identical can behave in opposite ways if one starts with soft water and the other with hard water, if one uses chloraminated tap water, if another has nitrate at the source, or if pH changes after the water sits.
Three Real Mistakes When Copying Aquariums Without Copying the Water
The substrate works against a high mineral load, exhausts sooner, and the aquarium becomes unstable.
The problem may not appear as an immediate alarm, but as stress, low margin, and chained mistakes.
The aquarium receives new load at every water change, and the aquarist blames the filter, substrate, or plants.
9. What to Test Before Setting Up an Aquarium
- Fresh pH and pH after 24 hours: shows whether the water changes after stabilizing.
- KH: helps read buffering capacity and pH stability.
- GH: gives a general hardness reading for fish, shrimp, snails, and plants.
- TDS or conductivity: does not identify every salt, but helps read mineral load and accumulation.
- Nitrate: important because nitrate can already enter with new water.
- Phosphate: useful when algae are recurrent or source water seems loaded.
- Chlorine or chloramine: essential if you use public tap water.
MACI Starting Water Sheet
Before buying fish or copying a routine, complete this sheet:
- Water source:
- Known treatment: chlorine, chloramine, filter, softener, storage tank, cistern:
- Fresh pH:
- pH after 24 hours:
- KH:
- GH:
- TDS/conductivity:
- Nitrate:
- Phosphate if available:
- Smell, color, sediment, or variation:
- Type of aquarium you want to build:
- First decision that changes after reading these values:
10. Which Decisions Change Depending on Your Water
Your source water can change which fish make sense, which plants will be easier, whether mixing with low-mineral water is useful, whether remineralization is needed, whether an active substrate makes sense, whether water changes help or add load, and whether you need a conditioner for chlorine or chloramine.
MACI does not try to make everyone use the same water. It asks each aquarium to be designed from its real starting point.
The International MACI Rule
Do not copy aquariums. Copy criteria. Start with your water.
Source water does not decide everything, but it conditions the beginning of the system. Before buying more products, restarting, blaming the filter, substrate, plants, or fish, look at the water you are adding.
Not because water has to be perfect. Because no living system can be understood well if you ignore the material it starts from.
Continue With MACI
If you are setting up an aquarium from zero, begin with the practical Easy-to-Run manual.
If you already have gasping fish, cloudy water, recurring algae, melting plants, or values you do not understand, go to the MACI Diagnostic Manual.
If you want to understand the full framework, enter the MACI homepage and continue from there into guides, books, and the official definition.
Official Sources Consulted
- EPA: chloramines and drinking water disinfection.
- EPA: private drinking water wells.
- CDC: guidelines for testing private well water.
- European Commission: drinking water.
- BOE: Royal Decree 3/2023 on drinking water quality in Spain.
- WHO/UNICEF Joint Monitoring Programme: water, sanitation and hygiene data.
- PAHO/WHO: water and sanitation in the Americas.
- Scottish Water: chloramination FAQs.