High Ammonia in New Tank What to Do

If your ammonia is above 0.25 ppm and you have fish in the tank, you’re in an emergency. Not “check back tomorrow” territory—RIGHT NOW emergency. Fish can die within 24-48 hours at high ammonia levels. Read the next section before you do anything else.

First: Are Your Fish Actually Dying Right Now?

Seriously, look at your tank. Are fish gasping at the surface? Hanging by the filter? Not moving much? Red gills?

If YES → Skip to “Emergency Protocol” below (do it NOW, then come back and read the rest).

If NO (fish seem okay) → Keep reading, but understand you’ve got maybe 12-24 hours before things get bad.

Emergency Protocol (Do This in the Next 30 Minutes)

That’s it. Those five steps will keep your fish alive for the next few days while we fix the actual problem.

Okay, But What IS Ammonia and Why Is My Tank Full of It?

Here’s the crash course:

Ammonia (NH₃) comes from fish waste, uneaten food, and anything rotting in your tank. It’s basically liquid poison. Even 0.5 ppm burns fish gills like you’re making them breathe bleach.

In a healthy tank, beneficial bacteria eat the ammonia and convert it to nitrite (also toxic), then other bacteria convert that to nitrate (way less toxic). This is called “the nitrogen cycle.”

Your new tank doesn’t have those bacteria yet. That’s the problem. It takes 4-6 weeks for enough bacteria to grow naturally.

Why New Tanks Get Ammonia Spikes (The Real Reasons)

I see the same mistakes over and over:

1. You added fish the same day you set up the tank
This is called “fish-in cycling” and it’s basically using your fish as test subjects while bacteria grow. Some fish survive it. Many don’t.

2. You added too many fish at once
Even if you waited a week or two, adding 10 fish to a new tank overwhelms the small bacterial colony that’s started growing. Bacteria can’t multiply fast enough to handle the ammonia spike.

3. You’re overfeeding
Beginners ALWAYS overfeed. I did it too. That flake you dropped that nobody ate? It’s sitting in the gravel rotting and creating ammonia.

4. You “cleaned” the tank too much
Did you rinse the filter in tap water? Congrats, you just killed all your beneficial bacteria with chlorine. Back to square one.

5. Your tank is too small for the bioload
5 goldfish in a 10-gallon tank will ALWAYS have ammonia problems. The waste production exceeds what bacteria can handle, even in a cycled tank.

What Ammonia Level Is Actually Dangerous?

Let me be blunt about this because a lot of guides sugarcoat it:

The Fix (Short-Term vs. Long-Term)

Short-Term: Keep Fish Alive This Week

Your goal right now is simple: keep ammonia under 0.25 ppm until bacteria grow. Here’s how:

How long will this take? Honestly? 3-6 weeks usually. Sometimes 8 weeks if things go wrong. Yeah, it sucks. But it beats waking up to dead fish.

Long-Term: Actually Fix the Problem

Water changes are a bandaid. They don’t fix the underlying issue (no bacteria). Here’s how to speed up bacterial growth:

Option 1: Bottled Bacteria (60% success rate)
Products like Seachem Stability, Tetra SafeStart, or API Quick Start. Do they work? Sometimes. Worth trying? Absolutely.

Dose daily for 7 days. Keep testing. If ammonia drops to 0 within 10-14 days, it worked. If not, you still need to wait for natural bacteria.

Option 2: “Seed” Your Tank (90% success rate)
Get a piece of used filter media from someone with an established tank (fish store, friend, local aquarium club). Squeeze it into your tank. You’re literally transferring billions of bacteria.

This cuts cycling time from 6 weeks to 2-3 weeks. Best method, hands down.

Option 3: Wait It Out (100% success rate, just slow)
Do nothing special. Just water changes + light feeding. Bacteria WILL grow eventually. Takes 4-8 weeks but it’s guaranteed.

Common Mistakes That Make It Worse

1. “I’ll just do bigger water changes”

Water changes dilute ammonia but don’t fix the root cause. I’ve seen people do 75% changes daily for MONTHS. Their tank never cycled because they kept removing the ammonia bacteria need to “eat” and multiply.

Aim for 50% max. You want some ammonia present (just not toxic levels) so bacteria have food to grow.

2. “I’ll add more bacteria bottles”

Overdosing bacteria doesn’t help. Once you hit the bottle’s recommended dose, more doesn’t make them grow faster. It’s like watering a plant—more isn’t always better.

3. “I’ll get a bigger filter”

Filter size doesn’t matter if there’s no bacteria IN the filter. A bigger filter with zero bacteria is just a bigger empty house.

4. “I’ll fast my fish for a week”

Fish can handle 2-3 days no problem. Maybe even 5-7 days. But extended fasting weakens their immune system and they get sick. Feed lightly—don’t starve them.

5. “I’ll remove the fish and let the tank cycle without them”

Where are the fish going? If you move them to an uncycled temporary tank, you’ve just created TWO tanks with ammonia problems.

Red Flags: When to Consider Returning Fish

Real talk: sometimes the kindest thing is admitting you’re not ready.

Consider returning fish to the store if:

• Ammonia stays above 1.0 ppm despite daily 50% water changes for 5+ days
• You can’t commit to testing + water changes daily for the next month
• Multiple fish are dying despite your best efforts (2+ deaths in 3 days)
• You have large/sensitive fish (goldfish, bettas, cichlids) in a small tank (<20 gallons)

Most fish stores will take returns within 7-14 days. It’s not failure—it’s being responsible.

Timeline: What to Expect

FAQ: Questions I Get Asked Constantly

Q: Can I just buy more fish once ammonia drops?

A: NO. Wait until the tank is fully cycled (ammonia 0, nitrite 0 for 7+ days). Then add 2-3 fish MAX. Wait 2 weeks. Add 2-3 more. Slow is safe.

Q: My test shows 0 ammonia but fish are still dying. Why?

A: Test nitrite. Bet it’s 2.0+ ppm. Nitrite is just as toxic as ammonia but appears later in the cycle. Same fix: water changes + Prime.

Q: Will live plants help?

A: A little. Plants absorb some ammonia. But they can’t handle a full bioload. Don’t rely on them as your main fix.

Q: Can I use ammonia remover pads/crystals?

A: They work as an emergency bandaid. But they can slow bacterial growth because they remove the ammonia bacteria need to eat. Use Prime instead.

Q: How long can fish survive at 0.5 ppm ammonia?

A: Days, maybe a week. But they’re suffering the entire time. Gills are burning. Stress is through the roof. Immune system crashes. Then they get ich or fin rot and die anyway.

The Honest Truth About Fish-In Cycling

Look, I know you already have fish. You can’t un-buy them. So let me be real with you:

Fish-in cycling sucks. For you AND the fish. You’re stuck testing daily, doing water changes daily, stressing about whether you’ll wake up to dead fish.

But thousands of people have done it successfully. I’ve done it three times (once on purpose, twice by accident when filters crashed). Your fish CAN survive if you’re diligent.

Here’s what you need:

• 30 minutes every day for 4-6 weeks (testing + water changes)
• Seachem Prime or equivalent ($10-15)
• A test kit ($25-35 for API Master Kit)
• The discipline to NOT add more fish until it’s done

Can’t commit to that? No judgment. Return the fish, cycle the tank properly with pure ammonia (no fish), THEN get fish in 6 weeks.