PH and Hard water

[gngrhill]

What should be the Ideal range for PH and mineral content (Hardness) of the water for most orchids ? I got some test strips ( made for fish water ) to test my water and got some confusing results.

[tropterrarium]

I shoot for pH in the 6.3-6.5 range, so a tad acidic off neutral 7. Mineral content: depends what you are growing, how you are growing (mounted vs. pots), and how you water. For fickle species, you try to get mineral content close to zero (TDS ~30, not sure how that translates to hardness). The less solutes there is in the water, the more touchy pH becomes, so the question arises, how much do you want to monitor your pH, TDS, hardness values.

For instance, when I add RO formulated fertilizer to my RO water (with TDS ~30), then I have to adjust pH with a few drops of KOH. In theory, that should not be necessary, because the RO fertilizer is made for RO water, but reality is different. I use both a colorimetric pH kit, as well as an electronic pH meter, which needs to be periodically calibrated.

If you don't want to fuss that much, then it may be a better strategy to use harder water with more pH buffer capacity, but flush your plants really well to get rid of salt build up.

I bet Ray will chime in as well.

[Subrosa]

Take it from a long time aquarium professional. Test strips designed for aquarium use are about as trustworthy as a politician. If you have municipal water you can easily get all the information about your water than you need. If you're on a well and need to do your own testing, liquid reagent kits are more reliable.

[ALToronto]

Don't test the water going in, test what comes out of the pot. You may find that you need to add some gypsum or limestone chips to your medium to moderate the pH.

[gngrhill]

Thanks all. I need to do some more work on this

[isurus79]

You should be able to get your required data from the municipal water supply website

[naoki]

I agree with Alla, it is more important to know what roots are experiencing than what you are pouring into. For example, there is a study of media acidification in Phalaenopsis (pH goes down after growing plants for a year or so). Even if the fertilizer is around pH of 5-6, the roots were experiencing pH of 3-4 (in sphag based media). But the researchers noted that even at the extremely low pH (almost like for Cypripedium actual), the plants weren't having problems. So, it is not known what would be the optimal pH for potted orchids. A lot of information about pH is coming from soil-based crop plants (which experience completely different root environment). The major part of acidification was also from the excretion of roots.

To measure the pH (and TDS) of pour through, one standard method is 1. fertilize (or irrigate) normally, 2. wait for 1 hour or so, 3. pour a small amount of pure water and catch the water coming out from the bottom, 4. then measure the pour-through water.

If you are going to keep truck of the long term change, I would standardize the amount of water you pour at the step 3 (e.g. 1/4 cp). Also I would measure the TDS of pure water before pouring and subtract the value from the pour-through value if your pure water isn't so pure.

With regard to TDS, lowest is the best if you are talking about the optimal. There is a range where plants can tolerate the concentration of solutes (plant roots can't absorb water if solute conentration in the surround area is too high). There is wide variation among species with regard to the tolerance. In any case, if you start with the pure water, you can add the mineral nutrients more.