Hard Water - Do I need RO?

My water is 450ppm out of the tap. I just watched a video that claimed anything over 300 is really hard. I have been adding nutrients that bring it up to 800ppm or 1.5 EC.

My girls appear to be growing fine (40 days in), but i notice my pH in my resevoir rises daily. From 5.8 to 6.4 over 24 hrs.

Should I consider an RO system with this kind of water? Would it mean less pH adjusting (I adjust nearly daily now).

An RO/DI unit would definetly reduce your costs for adjustment chemicals. For the cost of a unit, I would get one. You can get decent ones on eBay for around $60

My water is 350ppm out of the tap and i use it to grow hydro.

Tap mainly has calcium, magnesium, and silica in it, However, just because you Have 450ppm in your water doesn’t necessarily mean all 450ppm is available to the plant.

I add nutrients like the 350ppm doesn’t even exist in my water. For example, if i normally wanted to adjust some R/O water to 1000ppm, then i take it to 1350ppm with my tap water instead.

I do However still try not to cross 1600ppm like this. I have never had my water tested but if I had and I knew that everything in it was unavailable to the plant then I could take it up to 1900ppm, but i don’t know what’s in my water therefore i always keep it 1600ppm or less


That’s not terrible, but it should be a little more stable as long as ppms are above 500-600. I notice my reservoir will rise for the first 24 hours after topping off with my tap water or doing a reservoir change with my tap water but seems to stabilize after that

I’m using Heavy16 nutes which are supposed to be pH stable. I made a large fresh batch of nutes and it moved from 5.6 to 6.2 in 24hrs. I was hopping that an 8G batch would be more stable. My understanding is that we want some pH increases over time as that indicates that the plants are absorbing the negative ions.

But I’m not sure if I should be adding pH Down on a daily or bi-daily basis.

Maybe I should buy some distilled water and test that for a week first.



I’ve adjust mine anytime it moves out of the range that i want it in

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And you can only really test distilled water for TDS and not PH. Not enough solids to react with the electrodes.

More solids in your solution will generally move more slowly both to and away from your target PH but in general will migrate upwards over time. A larger reservoir will help as well.

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But wouldn’t distilled water act as a substitute for RO water? In both cases I’m assuming I would need to add calmag to bring up the ppms.

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Same for R/O water.