Can I use Vancouver tap water with semi-hydro?

[estación seca]

I let my drinking water stand overnight after drawing it from the faucet.

My tap water has a very high pH, and 600-1200 ppm dissolved solids. I mix 5-30 gallons of watering solution at a time. For many orchids I use about 20% water directly out of the tap, and 80% collected rain. I add a tiny amount of vinegar, then add fertilizer or growth adjuvants. With the high minerals in the tap water I don't need to use calcium additives.

For a few orchids needing fewer minerals in the water I use only a tiny amount of tap water plus rain, plus small amounts of fertilizer. I use the tap water for the calcium.

A fair number of my plants are watered by a sprinkler on a timer, with my awful water. They get soaked every morning. This keeps washing out the salts, so they don't accumulate. I have found that, even for a lot of plants preferring purer water, they do better watered this way rather than waiting for me to water them by hand, which sometimes doesn't happen on schedule when I have a long day at work. This also works well for bifoliate and drought-adapted Cattleya seedlings in net pots with little medium, plants like C. intermedia, harrisoniana, walkeriana.

I water other kinds of tropical plants with straight tap water. I occasionally get magnesium deficiencies. A lot of them are accustomed to a more neutral or even acidic root environment than I give them. A neutral or slightly acidic root environment makes most minerals easier to take up by the roots. I give those plants magnesium in the form of Epsom salts when I notice deficiencies. I don't try to make those grow to perfection because they already grow like weeds - for example, Passiflora quadrangularis.

I've only had one rainstorm here since February, and I'm down to my last two barrels of rain. I hope we get some rain this winter.

[spinrah]

Originally Posted by Clawhammer

Does anyone "rest" their water? My tap water (super pure PNW water) comes out of the tap between 7.5-7.8 before ferts. After resting 24 hours with aeration it is around 6.8 before ferts as CO2 is removed from the water by aeration. This effect is larger during the cold months as cold water absorbs more CO2.

Interesting - I will try that.

[Clawhammer]

Originally Posted by spinrah

Interesting - I will try that.

We have very similar water.

I used to keep discus fish, which require very pure water and stable pH, which is a challenge bc pure water doesn't have much buffering capability. Aging water is a requirement for those fish.

Some people's water goes up in pH, some go down as the water is rid of trapped gasses.

[Ray]

Originally Posted by Clawhammer

Does anyone "rest" their water? My tap water (super pure PNW water) comes out of the tap between 7.5-7.8 before ferts. After resting 24 hours with aeration it is around 6.8 before ferts as CO2 is removed from the water by aeration. This effect is larger during the cold months as cold water absorbs more CO2.

Maybe I am misunderstanding, but the pH does not drop due to loss of CO2, it does so because water absorbs it, it dissociates and forms the weak, carbonic acid, H2CO3.

With the median concentration of CO2 in air being around 400 ppm, the equilibrium pH in pure water is about 5.3.

[Clawhammer]

Originally Posted by Ray

Maybe I am misunderstanding, but the pH does not drop due to loss of CO2, it does so because water absorbs it, it dissociates and forms the weak, carbonic acid, H2CO3.

With the median concentration of CO2 in air being around 400 ppm, the equilibrium pH in pure water is about 5.3.

Hi Ray, I stand corrected. I am gassing off something that causes my pH to drop almost a point in 24 hours. Could I be gassing off the Sodium hydroxide my city adds to the water to raise pH?

[Roberta]

Can't be sodium hydroxide... that isn't volatile. Ammonia perhaps? Ray, you know a lot more about the chemistry and behavior of chloramine (chlorine + ammonium hydroxide, used for disinfection) than I do.