You installed a filter — pH still swings. You set up reverse osmosis — the water became "strange" and plants respond worse than before. Sound familiar? The equipment isn't the problem. The issue is that water has its own chemical composition — and until you know what it is, every solution is guesswork.
Quick Glossary
- pH — solution acidity (scale 0–14; plants prefer 5.5–6.5)
- EC — salt concentration in water (higher = more dissolved salts)
- KH — alkalinity; the water's resistance to pH change
- GH — hardness; calcium and magnesium content
- RO — reverse osmosis, a deep filtration system
- Ca — calcium, Mg — magnesium, K — potassium
Three Parameters That Determine Everything
KH — alkalinity. This is not the same as pH, though it sounds related. KH shows how strongly the water pulls pH upward and returns it after correction. High alkalinity is the main reason pH "won't hold." You correct it, it climbs back. You correct again — it climbs again. That's not a malfunction; it's the chemistry of your water.
GH — hardness (calcium and magnesium). Your water already contains Ca and Mg before you add any nutrient. If levels are high, a recipe designed for "empty" water will produce excess. Excess calcium blocks magnesium and potassium uptake. The plant looks deficient — even though the recipe is correct.
Source water EC — salt concentration in tap or well water before any nutrients are added. This is the baseline. Ignore it and your working solution EC will always exceed the calculated value — the plant gets more salt than you think.
All three parameters are measured with basic test kits or an EC/pH meter. Without these numbers, you cannot know what the problem actually is or what to do about it.
What Type of Water You Have — and What to Do
Normal water: EC < 0.4, low KH, stable pH. The simplest case. A mechanical filter plus carbon filter to remove chlorine is sufficient. The nutrient recipe accounts for background Ca and Mg — the system runs stably.
pH keeps rising — high alkalinity (KH > 5–6). A standard filter won't help. Alkalinity is neutralised by acidification — using nitric or phosphoric acid dosed directly into the tank. Important: the goal is not to "lower pH" but to neutralise carbonates (the mineral buffer in the water). If you add acid without neutralising the buffer, pH will rebound within hours.
Hard water: calcium > 120 mg/L, GH > 15°dH. The nutrient recipe is adapted around the background Ca and Mg — or a portion of the water is replaced with RO water. A salt-based softener is not an option: it replaces calcium and magnesium with sodium, which accumulates in the substrate and gradually poisons the root environment.
Well water or unknown composition. A full water analysis is mandatory — without it you cannot identify what needs correcting. A reverse osmosis system followed by remineralisation is the most common solution.
Chloramine in the water (used as a disinfectant instead of chlorine). Letting water stand does not help — chloramine does not evaporate the way chlorine does. A carbon filter with adequate contact time or reverse osmosis is required.
Reverse Osmosis: When It's Justified, When It's Overkill
RO is a membrane filter that removes nearly everything from water: salts, minerals, buffers. The output EC is close to zero — "bare" water with nothing in it. This provides maximum control: the nutrient recipe is built entirely from scratch with no dependence on source composition.
Justified when: water is complex (iron, sodium, seasonal variability), or you need precise batch-to-batch reproducibility — for example in a commercial recirculating system.
Overkill when: home grow setup, reasonably normal water, no need for absolute recipe precision.
Remineralisation After Reverse Osmosis: One Rule
"Bare" RO water is unstable — it has no buffer, and pH swings with any disturbance. Remineralisation returns the right minerals in the correct proportions. Simply adding CalMag is not enough: it raises Ca and Mg, but does not restore the buffer.
Simple rule: after remineralisation and mixing with nutrients, pH should settle in the working range and not shift more than 0.2 units over 12 hours. If it drifts — the remineralisation formula needs adjustment.
Three Mistakes That Cost the Most
Buying equipment before analysing water. A carbon filter for a hard water problem — money spent, problem stays. Analysis first, solution second.
Using a salt-based softener for irrigation water. Sodium accumulates invisibly in the substrate and causes problems weeks later — when the root cause is hard to trace.
A single water test for years. Municipal water composition changes seasonally. Well composition changes after heavy rain or flooding. A water analysis is valid for approximately one year.
How to Know Everything Is Configured Correctly
- After full preparation — filtration, correction, and mixing with nutrients — solution pH stays in the working range and does not drift more than 0.2 units over 12 hours without plants
- If it drifts — either alkalinity is not neutralised, or remineralisation is not calibrated correctly