pH, GH, KH, ammonia, nitrite and nitrate get thrown around constantly in aquarium forums, but many keepers never learn what each one actually measures or why it matters specifically for a planted tank. This is a practical reference: what each parameter tells you, the ranges that work well for most aquarium plants, and how to actually test for them without overcomplicating things.

Why Water Parameters Matter More in a Planted Tank

In a fish-only tank, water parameters mostly exist to keep livestock safe. In a planted tank, they do that too, but they also directly control how well your plants grow. pH affects which nutrient forms are available for roots and leaves to absorb, GH supplies the calcium and magnesium plants use for cell structure, and KH buffers pH swings that would otherwise stress both plants and fish. Getting these right is as much a growing decision as a safety one.

pH: Acidity and Alkalinity

pH measures how acidic or alkaline your water is on a scale of 0 to 14, with 7 being neutral. Most aquarium plants and community fish are comfortable in a range of roughly 6.5 to 7.5, which happens to be close to what many Indian municipal water supplies naturally sit at. pH is not something to chase aggressively with chemicals – large, fast swings are far more stressful to fish and plants than a stable pH that sits slightly outside the “ideal” range. If your water is consistently above 8 or below 6, it is usually better to choose plants and fish suited to that water than to constantly fight it with additives.

GH: General Hardness

GH measures the concentration of dissolved calcium and magnesium in your water, expressed in degrees of general hardness (dGH). These minerals are essential nutrients for plant cell walls and healthy growth, not just a fish-health number. Most planted tanks do well in a GH range of roughly 3 to 8 dGH. Water that is very soft (close to 0 GH, as some RO or heavily filtered water can be) may need a remineraliser added back in for plants and shrimp to get enough calcium and magnesium, while very hard borewell water common in parts of India may need dilution with RO water for the most sensitive plant and shrimp species.

KH: Carbonate Hardness

KH measures dissolved carbonate and bicarbonate ions, and its main practical role is buffering – resisting pH swings. A KH of roughly 3 to 6 dKH is a good target for most planted tanks. Very low KH (below 1–2 dKH) means pH can swing dramatically from something as simple as a CO2 injection schedule or a heavy feeding, which is a common hidden cause of stressed fish and stalled plant growth that keepers mistake for a different problem entirely. If your KH is very low, raising it slightly with a buffering product or crushed coral in the filter stabilises pH without needing constant intervention.

Ammonia, Nitrite and Nitrate

These three are the nitrogen cycle byproducts and are covered in full detail in our dedicated nitrogen cycle guide, but as a quick reference for testing:

• Ammonia: Should read 0 ppm in an established tank. Anything above 0.25 ppm is a warning sign worth investigating immediately.
• Nitrite: Should also read 0 ppm once cycled. Like ammonia, any detectable reading in a mature tank usually points to overstocking, overfeeding, or a filter that has been disturbed.
• Nitrate: The one parameter you want to see some of. Aim to keep it under roughly 30–40 ppm through a combination of water changes and plant uptake – a heavily and healthily planted tank often runs persistently low nitrate simply because the plants are consuming it as fast as it forms.

How to Actually Test These Parameters

Liquid reagent test kits are worth the small extra cost and effort over paper strips, particularly for ammonia, nitrite and KH, where strips are notoriously inaccurate. A master test kit that covers pH, ammonia, nitrite, nitrate, GH and KH in one box is the most cost-effective way to start and will typically last many months of regular testing. Test at a consistent time relative to feeding and dosing, since ammonia and nitrate in particular fluctuate meaningfully over a day. For a new tank, test every one to two days during cycling; for an established, stable tank, weekly or before/after any change (new plants, new fish, a fertiliser change) is usually enough.

Target Ranges at a Glance

• pH: 6.5–7.5 for most community planted tanks
• GH: 3–8 dGH
• KH: 3–6 dKH
• Temperature: 22–28°C for most tropical planted tanks
• Ammonia: 0 ppm
• Nitrite: 0 ppm
• Nitrate: Under 30–40 ppm, ideally kept low by plant uptake and regular water changes

Adjusting Parameters Safely

The most common mistake with water parameters is over-correcting quickly. Large, sudden shifts in pH, GH or KH stress fish and plants far more than gradually moving toward a better range. If you need to soften very hard borewell water, blend it with RO water gradually rather than switching all at once. If you need to raise a very soft or low-KH tank, add buffering minerals in small doses and retest before adding more. For most Indian tap and municipal water supplies, parameters are already close enough to plant-friendly ranges that no major adjustment is needed at all – testing first before reaching for additives saves both money and unnecessary stress on your tank.

Once your parameters are dialled in, the next piece of the puzzle is making sure plants are actually getting fed correctly within those parameters – see our guide on how often to fertilise aquarium plants for a practical dosing routine.

Frequently Asked Questions

Do I need to test water parameters if my tank looks healthy?

Yes, at least occasionally. Ammonia and nitrite spikes are invisible to the eye, and slow parameter drift (rising nitrate, falling KH) often shows up as subtle plant or fish stress well before it becomes visually obvious. A monthly check on an established tank is a reasonable minimum.

Is RO (reverse osmosis) water necessary for a planted tank in India?

Not usually. RO water is mainly useful where borewell water is extremely hard or has other quality issues, or for keeping sensitive soft-water species like certain shrimp. Most municipal supplies and moderate borewell water work fine for common planted-tank species without RO treatment.

Why does my pH keep dropping between water changes?

This is usually a sign of low KH, meaning your water has little buffering capacity against the natural acids produced by fish waste, CO2 injection and decomposing organic matter. Raising KH slightly stabilises pH between water changes.