I am looking to redo one of my tall 40gal custom tanks. I want it to have crazy looking fish that you do see often. 

what should I get?! 

I got this angelfish a few months back. New to angelfish what kind do you think they are?

Also male or female?

If you’re setting up your first tank, cycling your aquarium is the most important thing you need to understand. Without it, your fish could suffer — or worse. This guide will break down the aquarium cycle in simple terms and help you avoid beginner mistakes that lead to toxic water and stressed-out fish. Whether you're using live plants, fishless cycling, or hardy starters like zebra danios, this article will walk you through how to cycle the right way.

What Does “Cycling” an Aquarium Mean?

Cycling is the process of establishing beneficial bacteria that convert toxic fish waste into less harmful substances. These bacteria live in your filter, substrate, and decorations — and they’re your tank’s built-in water treatment crew.

Here’s the simplified breakdown:

1. Ammonia is produced from waste and leftover food
2. Bacteria convert ammonia into nitrite (still toxic)
3. Another set of bacteria converts nitrite into nitrate (less toxic)
4. Nitrate is then removed through water changes or plants

✅ Quick Recap:

• No cycle = toxic water
• A cycled tank keeps ammonia and nitrite at 0 ppm
• Nitrate levels should be kept below 20–40 ppm

How to Cycle Your Aquarium

There are a few methods to cycle your tank. Here’s how each works:

🐠 Option 1: Fish-In Cycling

This method uses hardy fish (like zebra danios) while carefully managing water quality.

Steps:

• Add a small number of hardy fish
• Test water daily for ammonia and nitrite
• Perform partial water changes (25–50%) to keep levels safe
• Add bottled beneficial bacteria (e.g., FritzZyme, Seachem Stability)

Pros: Fast, easy for beginners
Cons: Risk of harming fish if you're not consistent

💧 Option 2: Fishless Cycling

The safest and most ethical method, especially if you’re not in a hurry.

Steps:

• Add ammonia manually (pure, unscented)
• Monitor ammonia → nitrite → nitrate over time
• When ammonia and nitrite hit 0 ppm within 24 hours of dosing, your cycle is complete

Pros: No fish are harmed, more control
Cons: Takes 2–6 weeks and requires patience

🌱 Option 3: Live Plants & Seeding

Aquascaped tanks with live plants and seeded media (from an established tank) can kickstart your cycle.

Tips:

• Use substrate or filter media from an established tank
• Add fast-growing plants (like hornwort or water wisteria)
• Still test water regularly

Pros: Natural and beautiful start
Cons: May not work alone for high bioloads

How Long Does It Take to Cycle?

• With bacteria additives: ~1–2 weeks
• Without additives: 3–6 weeks
• With seeding + plants: Often faster, depends on bioload

There’s no magic number — only your test kit can tell you when it’s ready.

✅ Quick Recap:

• Speed depends on your method
• Test kits are mandatory
• Rushing leads to dead fish and frustration

Tools You Need

• Liquid test kit (API Freshwater Master Kit is best)
• Dechlorinator (like Seachem Prime)
• Beneficial bacteria additive (optional but helpful)
• Patience (not sold in stores 😅)

🧪 Need help choosing a test kit? Read our guide: Best Liquid Test Kits for Aquariums

How to Know When It’s Done

You’ll know your tank is fully cycled when:

• Ammonia = 0 ppm
• Nitrite = 0 ppm
• Nitrate is present (5–40 ppm)
• You can dose ammonia and see it processed within 24 hours

Then — and only then — it’s safe to add fish.

Common Mistakes to Avoid

❌ Adding all your fish at once
❌ Not testing regularly
❌ Cleaning the filter media with tap water
❌ Thinking your tank is cycled just because the water is clear

FAQs

Q: Do I need to cycle if I use live plants?
A: Yes — plants help, but they don’t fully replace the bacterial cycle.

Q: What if I already added fish?
A: That’s okay! Switch to a fish-in cycle method and test daily.

Q: Can I speed up the cycle?
A: Yes — use bottled bacteria or seeded media from an established tank.

Final Tips & Takeaways

Cycling is where aquarium success begins. A tank with no ammonia or nitrite is a safe, stable home for your fish — and helps avoid stress, disease, and early losses. Be patient, test regularly, and let nature do its thing.

📚 Further Reading

🗨️ Question for You

Are you cycling your first tank or helping a friend set one up?
Let us know in the comments or post your journey in the UndergroundAquarium.com forum!

Nitrites (NO₂⁻) are a toxic compound that can quickly threaten the health of your fish — especially in newly cycled or poorly maintained aquariums. While often misunderstood by beginners, understanding nitrites is crucial to keeping your tank balanced and your fish safe.

What Are Nitrites?

Nitrites are a natural part of the nitrogen cycle. After fish waste, uneaten food, and decaying plants break down into ammonia, beneficial bacteria (Nitrosomonas) convert that ammonia into nitrite. While this is a necessary step, nitrites are still dangerous — they must then be converted into nitrates by a second set of bacteria (Nitrobacter) to make the water safer.

✅ Quick Recap:

• Ammonia → Nitrite → Nitrate
• Nitrites come after ammonia in the nitrogen cycle
• Still highly toxic to fish

Why Nitrites Are Dangerous

Nitrites bind to hemoglobin in a fish’s blood, preventing it from carrying oxygen — a condition called “brown blood disease.” Even low levels can cause stress, while higher levels can be fatal.

⚠️ Symptoms of Nitrite Poisoning:

• Gasping at the surface
• Lethargy or odd swimming
• Loss of appetite
• Red or inflamed gills
• Clamped fins

🎯 Safe Nitrite Level:

• 0 ppm — anything above this is cause for concern

✅ Quick Recap:

• Nitrite poisoning affects oxygen delivery
• Anything above 0 ppm is dangerous
• Symptoms show up fast in sensitive species

What Causes Nitrite Spikes?

• New Tank Syndrome (cycling not complete)
• Overfeeding
• Overstocking
• Poor filtration
• Sudden disruption of beneficial bacteria (medications, deep gravel cleans, etc.)

📉 How to Reduce Nitrites Quickly:

• Immediate 25–50% water change
• Add dechlorinated water with Prime or similar conditioner
• Reduce feeding temporarily
• Add beneficial bacteria supplements
• Check filter functionality and media

✅ Quick Recap:

• Spikes are common in new tanks
• Fast response is critical
• Regular water testing prevents surprises

How to Prevent Nitrite Issues

• Always cycle your tank fully before adding fish
• Use a liquid test kit (not strips) to monitor nitrite, ammonia, and nitrate
• Perform weekly water changes and avoid overfeeding
• Keep filters cycled and avoid fully replacing all media at once

💡 Pro Tip: A high-quality test kit like the API Freshwater Master Test Kit should be part of every aquarist’s toolkit.

✅ Quick Recap:

• Prevention is easier than treatment
• Liquid test kits are a must
• Cycling your tank properly is non-negotiable

FAQs

Q: Are nitrites as bad as ammonia?
A: Yes. They may not burn gills the way ammonia does, but they block oxygen and are just as deadly.

Q: Can plants help reduce nitrites?
A: Not directly. Plants absorb nitrate, not nitrite — but they can help stabilize overall water quality.

Q: How long do nitrite spikes last?
A: In a cycling tank, it can take days to weeks. In a mature tank, it should be resolved in 24–48 hours with proper care.

Final Tips & Takeaways

• Test nitrites regularly, especially in new tanks
• Zero is the only safe level
• Act fast if you see a spike
• Cycling, maintenance, and filtration are your first line of defense

📚 Further Reading & Resources

• How to Cycle Your Aquarium
• Best Liquid Test Kits for Aquariums
• Understanding Ammonia Spikes

🧪 References

• Seachem. “Nitrite Toxicity in Freshwater Aquaria.”
• API Fishcare. “The Nitrogen Cycle Explained.”
• U.S. EPA. “Water Quality Criteria – Nitrite.”

🗨️ What About You?

Have you ever dealt with a nitrite spike? What’s your go-to method for keeping it under control?
Drop a comment or join the discussion in the UndergroundAquarium.com forum!

A couple happy Angelfish and a BN Pleco