Reference
Aquarium water chemistry, explained
Six numbers describe almost everything about your water. Here is what each one means, the ranges different tanks want, and how they fit together, starting with the two everyone confuses.
TL;DR, Aquarium water chemistry
Six numbers describe almost everything about your water. Temperature and pH set the basic conditions; KH is the buffer that keeps pH steady; GH is the calcium and magnesium plants and shrimp need; and ammonia, nitrite and nitrate track the nitrogen cycle. The trap is confusing GH and KH, which measure different things. You rarely need to chase a perfect pH; you need stable, sensible parameters that suit the species you keep. Soft-water fish and caridina shrimp want low, gentle numbers, hard-water livebearers and neocaridina want more mineral. Match the tank to the fish, then keep it stable.
GH and KH are not the same thing
This is the single most common mix-up, so it is worth clearing up first. General hardness and carbonate hardness both have "hardness" in the name, but they measure different things and you adjust them separately.
The parameters, one by one
Temperature
°CHow warm the water is, held by a heater on a thermostat.
Why it matters. Sets metabolism, oxygen levels and which species can live together. Swings stress fish and trigger disease more than any single wrong value.
Typical range. 22 to 26°C suits most community tropicals.
Adjusting it. A reliable heater and, in hot climates, a fan or chiller. Change it slowly, never in jumps.
pH
pHHow acidic or alkaline the water is, on a 0 to 14 scale where 7 is neutral.
Why it matters. Species evolved for a range, and extreme or unstable pH stresses them. Stability matters far more than hitting an exact number.
Typical range. 6.5 to 7.5 covers most community tanks. Blackwater fish prefer lower, hard-water fish higher.
Adjusting it. Don't chase it with pH-down bottles, which swing it dangerously. Use the water source, KH and CO2 to set it, then leave it stable.
Carbonate hardness
KHThe carbonate and bicarbonate buffer in the water, measured in dKH.
Why it matters. KH is what stops pH from crashing. Low KH means an unstable pH that can swing overnight; higher KH holds it steady.
Typical range. 3 to 8 dKH is a safe, stable band for most tanks. Caridina shrimp want very low KH.
Adjusting it. Raise it with crushed coral, aragonite or a KH buffer. Lower it by cutting it with RO water.
General hardness
GHThe dissolved calcium and magnesium in the water, measured in dGH.
Why it matters. These are minerals plants use and shrimp need to build their shells and molt. Too soft and shrimp fail to molt and plants show deficiencies.
Typical range. 4 to 8 dGH suits most planted community tanks; neocaridina shrimp want 6 to 8, caridina lower.
Adjusting it. Raise it with a GH or shrimp remineraliser containing calcium and magnesium. Lower it by cutting with RO water.
Total dissolved solids
TDSA rough measure of everything dissolved in the water, in ppm, read with a cheap pen meter.
Why it matters. Handy for shrimp keepers and RO users to track stability and spot drift, since it moves with hardness and buildup.
Typical range. Species-dependent; caridina shrimp keepers often target 100 to 150 ppm from remineralised RO.
Adjusting it. It follows your remineralisation and water changes. Rising TDS between changes flags evaporation and buildup.
Ammonia
NH₃The first and most toxic nitrogen waste, from fish and rotting food.
Why it matters. Even a small amount burns gills and kills fish. In an established tank it should always read zero.
Typical range. 0 ppm, always, in a cycled tank.
Adjusting it. Any reading means a water change now and a look at the cause: overfeeding, overstocking, or an uncycled tank.
Nitrite
NO₂⁻The second nitrogen stage, still toxic, produced as bacteria break down ammonia.
Why it matters. Also lethal to fish. In a cycled tank it reads zero; seeing it means the cycle is incomplete or has crashed.
Typical range. 0 ppm in a cycled tank.
Adjusting it. Water changes to protect fish, and let the bacteria catch up. Common during cycling.
Nitrate
NO₃⁻The end of the nitrogen line, far less toxic, that builds up over time.
Why it matters. Tolerable in moderation but a stress and algae driver when it climbs. It is what water changes and plants remove.
Typical range. Keep it under about 20 to 40 ppm; planted tanks often run it as a nutrient around 10 to 20.
Adjusting it. Water changes bring it down; fast plants use it up. Rising nitrate is the normal sign of a working, stocked tank.
Target ranges by tank type
There is no universal 'correct' water. Pick the row that matches what you want to keep, then set the tank to it and hold it steady.
| Tank type | pH | KH | GH |
|---|---|---|---|
| Community plantedThe flexible middle ground most tetras, rasboras and gouramis are happy in. | 6.5–7.5 | 3–6 | 4–8 |
| Soft / blackwaterWild-type tetras, apistogramma and chocolate gouramis; RO water plus botanicals. | 5.5–6.8 | 0–3 | 1–4 |
| Hard-water livebearerGuppies, mollies, platies want mineral-rich, harder water. | 7.2–8.2 | 6–12 | 10–20 |
| Neocaridina shrimpCherry-type shrimp; steady GH is critical for molting. | 6.5–7.5 | 2–5 | 6–8 |
| Caridina shrimpCrystal and bee shrimp; low KH on active soil, RO remineralised carefully. | 5.5–6.5 | 0–2 | 4–6 |
How they fit together
The parameters pull on each other. KH props up pH, so if you inject CO2 (which forms a weak acid and lowers pH) you need enough KH to keep that drop steady rather than a crash. GH and KH move together in most tap water but can be set independently with RO water and remineralisers. Temperature affects how much oxygen the water holds and how fast everything, including the nitrogen cycle, runs. And ammonia, nitrite and nitrate are the running score of that cycle: the first two should sit at zero, and nitrate is what you export with water changes. Change any of them slowly. Fish handle a steady value they weren't born for far better than a sudden swing toward the 'right' one.
Frequently asked questions
Direct answers to the questions search engines and AI assistants surface most often about this species.
What is the difference between GH and KH?
GH (general hardness) is the calcium and magnesium in the water, the minerals plants and shrimp need. KH (carbonate hardness) is the buffer that keeps pH stable. They are different measurements: you can have soft water (low GH) that still resists pH swings (higher KH), or vice versa. Test and adjust them separately.
What pH should my aquarium be?
For most community tanks, anywhere from 6.5 to 7.5 is fine. A stable pH in a sensible range beats a 'perfect' number that swings. Match it to your species: soft-water fish prefer lower, hard-water fish higher.
Should I use pH-down products?
Generally no. Acid buffers give a temporary drop that rebounds and can swing pH dangerously, which is worse than a stable 'wrong' value. Set pH through your water source, KH and CO2 instead, and keep it steady.
Why does my pH crash overnight?
Almost always low KH. With little carbonate buffer, acids from the substrate and CO2 pull pH down and it swings. Raise KH a little with crushed coral or a buffer to stabilise it.
How do I soften hard tap water?
Mix or replace it with RO (reverse osmosis) water, then remineralise back to the GH your fish or shrimp want. That gives you full control over both hardness and buffering, rather than fighting the tap.