API Freshwater Master Test Kit
$$The standard liquid test kit — ammonia, nitrite, nitrate, pH. Hundreds of tests per kit.
This is the cheat sheet I wish someone had handed me on day one. It's organized by parameter, with the target range, danger zone, and the action to take when something reads off. Bookmark it for the next time you draw a sample at 11 PM and need to remember what 0.5 ppm of nitrite means.
The four critical parameters
| Parameter | Target | Danger zone | Action if elevated |
|---|---|---|---|
| Ammonia (NH₃) | 0 ppm | >0.25 ppm — acutely toxic | 50% water change; dose Seachem Prime; check filter; reduce feeding |
| Nitrite (NO₂⁻) | 0 ppm | >0.25 ppm — acutely toxic | 50% water change; dose Prime; suggests cycle disruption |
| Nitrate (NO₃⁻) | 5–20 ppm | >40 ppm — chronic stress | 25–50% water change; live plants help long-term |
| pH | 6.5–7.8 stable | swing >0.5 in 24 hours | Don't chase; stable wrong-number beats unstable correct-number for most species |
The hardness parameters
| Parameter | What it measures | Target (most species) | Notes |
|---|---|---|---|
| GH | General hardness — dissolved Ca and Mg | 4–12 dGH | Higher for livebearers and African cichlids; lower for tetras, discus |
| KH | Carbonate hardness — buffering capacity | 3–8 dKH | Low KH means pH can crash; add baking soda to raise |
The physical parameters
| Parameter | Target | Notes |
|---|---|---|
| Temperature | 76–80°F tropical / 65–72°F coldwater | Stable matters more than exact. Heater + controller for safety. |
| Dissolved oxygen | 5+ ppm | Surface agitation matters more than air stones. Floating plant mats reduce gas exchange. |
Species-specific targets
| Species | Temp | pH | GH | Notes |
|---|---|---|---|---|
| Betta | 78–80°F | 6.5–7.5 | 5–20 | Adaptable; gentle filter flow critical |
| Neon / cardinal tetra | 74–80°F | 5.5–7.0 | 1–10 | Prefers soft, slightly acidic |
| Guppies / livebearers | 75–82°F | 7.0–8.0 | 10–20 | Like harder, slightly alkaline water |
| Corydoras catfish | 72–78°F | 6.5–7.5 | 4–10 | Hates high temps; smooth substrate |
| Goldfish (fancy) | 65–72°F | 7.0–8.0 | 8–20 | Coldwater; very high bioload |
| African cichlids (Mbuna) | 76–82°F | 7.8–8.6 | 10–25 | Hard, alkaline rift lake water |
| Discus | 82–86°F | 5.5–7.0 | 1–8 | Soft, warm, immaculate water |
| Cherry shrimp | 68–78°F | 6.5–8.0 | 6–15 | Very sensitive to copper |
Adjusting parameters when needed
To lower nitrate
- Water changes (25–50% weekly)
- Live plants — especially fast growers like hornwort, water sprite, pothos roots in the filter
- Reduce feeding
To raise pH and KH
- Baking soda (sodium bicarbonate): a small dose per 50 gallons raises KH measurably
- Crushed coral or aragonite in the filter — slow, gentle, ongoing buffer
- Reverse osmosis water with KH+ remineralization for specific targets
To lower pH and KH (carefully)
- Driftwood — releases tannins, gentle pH drop
- Indian almond leaves — same mechanism, plus mild antibacterial
- Peat moss in the filter — old-school but effective
- RO/DI water blended with tap to dilute mineral content
Seachem Prime Water Conditioner
$Neutralizes chlorine and chloramine; binds ammonia for ~24 hours. Essential emergency tool.
API GH & KH Test Kit
$Add-on test for hardness — essential for planted, shrimp, and African cichlid tanks. Not in the Master Kit.
The diagnostic checklist
Fish acting strange, no obvious cause? Run this list:
- Test ammonia and nitrite — should both be zero
- Test nitrate — should be under 40 ppm
- Check temperature — within range for the species?
- Check pH — stable, or fluctuating?
- Last water change — when, and how much?
- Filter — running normally, media not clogged?
- Anything new in the tank in the last 2 weeks? (new decor, new fish, plant, medication)
For step-by-step cycling, see our fishless cycle protocol. For water change schedule, see our water change guide.
FAQs
What's the perfect pH for a community tank?
There isn't one. Stability matters more than exact number for most beginner species. Whatever pH your tap water naturally settles to (anywhere 6.5–7.8) is fine for tetras, rasboras, corys, and most popular community fish.
Why is my nitrate always high?
Either you're underchanging water (do 25–50% weekly), overstocked, or overfeeding. Live plants help significantly long-term. Some tap water comes in with high baseline nitrate, which sets a floor you can't go below.
How do I lower ammonia quickly in an emergency?
Large water change (50%+) with dechlorinated, temperature-matched water plus a full dose of Seachem Prime. Prime binds ammonia for ~24 hours, buying you time to find the underlying cause.
What's the safest way to acclimate fish to a different pH?
Drip acclimation — slow water mixing over 1–2 hours via airline tubing. Sudden pH shifts of more than 0.3 cause stress; a drip rig is cheap insurance for any new arrival.
Heads-up: AquariumSetup.co participates in the Amazon Associates and eBay Partner Network programs. We may earn a commission on qualifying purchases at no extra cost to you. We only recommend gear we believe is genuinely useful to beginners.