A fresh RO filter can make a grower second-guess the whole feed program. Your starting EC drops close to zero, your pH moves easier, and the water no longer carries the calcium and magnesium that may have been coming in with tap water. So, does reverse osmosis remove minerals? Yes. That is the point of it.
For indoor growers dealing with hard water, high sodium, chlorine, or an unknown municipal water report, reverse osmosis gives you a clean starting point. It also means you need to put the right minerals back in through your nutrient program. RO water is not a complete plant feed. It is blank water waiting for a measured feed.
What Reverse Osmosis Removes From Water
An RO system pushes water through a membrane that rejects most dissolved material. That includes the calcium, magnesium, bicarbonates, sodium, iron, and other ions that show up as EC or ppm on a meter. It also reduces many contaminants that can make a feed hard to control.
The exact result depends on the membrane, water pressure, filter condition, and what was in the source water to begin with. Check the water coming out with an EC meter rather than guessing. A working RO system often produces water with very low EC, but it is not automatically zero.
What it does not do is make nutrients unnecessary. Plants still need nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, and trace elements. With RO water, those minerals need to come from the base nutrient and, when needed, a specific additive.
Why RO Water Changes Your Feed
Tap water can contribute a meaningful amount of calcium and magnesium before you ever open a nutrient bottle. Sometimes that is useful. Often, especially with hard water, it causes problems because you do not know the ratio or how much sodium and bicarbonate came along with it.
RO takes that variable out. That gives you better control, but it puts the responsibility back on the grower. If the base nutrient is mixed at the correct rate, it should supply the core mineral profile for the medium. Do not treat RO water like tap water and assume there is background calcium or magnesium available.
The other change is pH behavior. Tap water with a lot of bicarbonate has alkalinity, which resists pH movement. RO water has very little alkalinity. A small amount of pH adjuster can move it quickly, and the final pH should be checked after all nutrients and additives are mixed.
For hydro and coco, measure EC and pH every time you mix a reservoir. In soil and raised-bed containers, the same clean-water principle applies, but do not chase runoff numbers the way you would in a recirculating hydro system. Watch the plant, keep the feed consistent, and avoid piling on additives without a reason.
Start With the Right Bionova Base Feed
The base feed goes into RO water first. Pick it for the root zone, not for the crop name.
Soil: Bionova Soil-SuperMix
For soil, use Bionova Soil-SuperMix as the foundation. It is made for soil-grown plants and supplies the macro and micronutrients that RO water no longer brings in. Mix the base nutrient into the water completely before checking EC and pH.
Soil has some nutrient-holding capacity, so a living or amended mix may not need a heavy mineral correction right away. But plain RO water still does not provide calcium or magnesium on its own. If your plant shows a real need for one of those elements, correct that element directly instead of changing the whole base feed.
Coco: Bionova Coco Forte A+B
Coco is less forgiving when calcium and magnesium are out of balance. It holds and exchanges cations differently than soil, and the root zone needs a steady, complete feed. Use Bionova Coco Forte A+B for coco, mixed in the correct order and fully diluted before the next part goes in.
Do not combine concentrated Part A and Part B in the same measuring cup or bottle. Add one to the reservoir, mix well, then add the other. Starting with RO water makes your input EC easier to read, which is useful when dialing in a coco program.
Hydro: Bionova Hydro-SuperMix
For deep water culture, drip hydro, rockwool, or other hydroponic systems, use Bionova Hydro-SuperMix. Hydro gives you the least buffer at the root zone. The water and feed you mix are what the plant sees, so clean RO water and a complete base nutrient are a practical pairing.
Keep the reservoir mixed and verify EC and pH after the full formula is in. If the EC rises in the tank while water level falls, the plant may be taking up more water than nutrients. If EC falls quickly, it may be feeding harder. Those readings tell you more than a fixed calendar ever will.
Add Back Only the Mineral You Need
A low EC number from RO water does not automatically mean you should add every mineral bottle on the shelf. Use the base nutrient first. Then make a correction based on your water, medium, crop stage, and what the plant is actually doing.
Bionova Ca 15 is the direct choice when calcium needs to be increased. Calcium supports new growth and cell structure, and it is especially relevant in RO-fed coco and hydro where there is no tap-water calcium in the background. Use it as a targeted adjustment, not as a replacement for a balanced base nutrient.
Bionova MgO 10 is for magnesium. Magnesium sits at the center of chlorophyll, and a shortage can show up first on older leaves because the plant can move magnesium to newer growth. Before adding it, rule out root-zone pH problems and overfeeding. A plant can look deficient when the nutrient is present but unavailable.
If a feed needs a specific potassium or phosphorus adjustment, use Bionova K 20 or Bionova P 20 rather than changing multiple inputs at once. That is the advantage of a single-mineral program. You can make one correction and see what changed.
For trace-element support where a true micronutrient correction is needed, Bionova MicroMix keeps the adjustment focused. Do not add it just because your water is RO. Your base nutrient already carries trace elements. Use MicroMix when the situation calls for it and keep notes on what you changed.
A Simple RO Mixing Order
The cleanest way to run RO water is to stay consistent. Fill the reservoir with RO water, then add the correct Bionova base nutrient for soil, coco, or hydro. Mix thoroughly. Add a targeted mineral product only if your program calls for it. Then check EC, allow the solution to settle briefly, and adjust pH last.
For most hydro and coco work, growers commonly keep the finished solution in the general pH 5.5 to 6.2 range. Soil feeds are usually run a little higher, often around pH 6.2 to 6.8. The right point within those ranges depends on the medium and what the plant has been receiving. Consistency beats daily swings.
Use an EC meter you trust. RO water lets you see the mineral concentration you add, but an inaccurate meter turns that advantage into false confidence. Calibrate the meter, keep the probe clean, and write down your starting water EC, feed EC, pH, and any additives used.
When Tap Water May Still Be Fine
RO is not mandatory for every grow. If your tap water has a manageable EC, low sodium, reasonable alkalinity, and a mineral profile that works with your base nutrient, it can be used. The problem is that many growers do not know what is in it, and the water can change by season or municipality.
If tap water starts at a high EC, has heavy hardness, or causes your pH to fight you every watering, RO gives you control. It is also useful when you want repeatable recipes across different runs. Start clean, build the feed deliberately, and avoid trying to compensate for mystery minerals.
The next move is simple: test your source water, choose the Bionova base feed that matches your medium, and use Ca 15, MgO 10, K 20, P 20, or MicroMix only when your feed actually needs that correction. B Dubb Grows stocks the mineral inputs for growers who want to know exactly what is going into the root zone.
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