Hard water pH down

OK, so here's the deal with hard water. It generally has a bunch of bicarbonate that needs to countered with acid. So what are your economical choices?

Hydrochloric acid

Now correct me if I'm wrong but this is probably a bad choice. Chlorine is known to burn plant tips I've heard in excess of 20ppm.

In one scenario you use 2mL of 10% HCl to lower the pH of one gallon of water. 10% means weight per volume as grams per 100 mL in this case. Thats 10g per 100mL or 0.1g per 1mL so 0.2g per gallon of your water is HCl. That's the same as 200mg (note: the molecular weight of HCl is almost entirely chlorine so the hydrogen's contribution is negligible.) 200mg per 3.7854L is over 50ppm, more than double enough to cause tip burn.

You could remove the chlorine by letting it sit out, adding vitamin c(this will also lower the pH if using absorbic acid), etc. If not, even if you don't get tip burn you will fry the
beneficial bacteria.

Sulfuric and phosphoric acids

These can be used if accounted for in your nutrients. You need to find out how much acid is necessary to lower your regular water as this will be the highest concentration necessary and account for that in your nutrient formulation.

Some hard water nutrients may already do this.

Thoughts?

Nitric acid!

Nitric acid will work, but I don't grow the same plants you do so $100 for a bottle of the stuff is a little excessive lol.

Where do up you get that $100 price tag from? I pay the same for a bottle of nitric acid as phosphoric acid. Some cannabis nutrient brands call the nitric acic ph down veg/grow and the phosporic acid ph down bloom/flower, bottle has the same price, about 10 bucks.

The $100 price tag comes from Ebay as I looked at nitric acid before when I entertained the idea of using it to make magnesium nitrate. I've never really looked at pH up or down products sold specifically for your plant but from what I've seen in these forums previously I always assumed they were all phosphoric acid.

FWIW to lower the pH of my water for my cherry blossom trees it takes ~2 mL of 22-25% HCl so I prefer larger quantities of strong acids.

you're correct about your concerns about HCl, although it's not a serious issue. The Cl- ions will compete with the NO3- ions somewhat, but probably only a negligible amount. Nitric acid would be better than hydrochloric acid because while they're both strong acids, nitric acid provides food.

As a rule of thumb (even with humans and animals), any ions you eat that doesn't benefit you should just be automatically considered toxic and competing for ions that do something useful. Cells have channels meant to absorb certain types of ions (you know beta blocker drugs?). Na+, K+, and NH4+ all use the same channel.

For providing micro nutrients, sodium salts make sense because of how little you need (like sodium molybdate or sodium borate), but it would not make sense to use sodium hydroxide for pH up (assuming you did need pH up for something) because then you'd be using an appreciable amount of it. KOH in that case would obviously be a better choice because it's food instead of something that competes with food.

That being said, sodium hydroxide would be a better choice than baking soda... ugh........

Oh, for nitric acid, I'm currently just using technaflora pH down. I can't find another brand that uses nitric acid. That's one of those products where having the safety bottle is enough of a convenience where I just get a diluted bottle.

I used to buy phosphoric acid ph down, and use that during the veg period as well. Since last cycle I use only nitric acid because I rather add N than P, and it makes some of the calcium that makes the water hard available in a form the plant can take up. It's working out great. I no longer have to correct the pH of my nutrient solution, I no longer need pH up either.

How about creating some nitric acid? Wouldn't that be super cheap? Any downsides @churchaze?

I'm not sure if i trust even myself to make nitric acid in my home.. lol.

All the dry salts are relatively safe, but the nitric acid requires serious care when handling and storing. Wear a pair of goggles over another pair of goggles!! (just kidding)

Yeah nitric acid is some strong stuff. If you're going to make your own nitric acid there are two ways and both give off toxic fumes that can seriously maim or even kill you..I don't think a mask will protect you from the fumes so you need to have enough ventilation that they're all completely pulled away. Then you need to take into account the amount you're using, since it wont be pure. You can do this by making a stock solution of say sodium hydroxide and adding an indicator then back titrating the nitric acid to find out your concentration...it's all just a lot of work. Sulfur is safe up to 1000ppm for your plant so if you have hard water and you're formulating your own nutrients, provided your water isn't chock full of sulfur already then sulfuric acid should do fine.

I looked at the MSDS of GH pH down powder. I'm not sure off the top of my head of those ingredients would make phosphoric acid in aqueous solution but I don't think it would. It has citric acid in it.

Phosphoric acid is a bad solution anyway since the plants you're growing are much more intolerant of excess K than S.

Note to self: Store pH pen in calibrated solution and just rinse it with DI water between uses...or it will become uncalibrated and mess stuff up.

If you're going to use sulfuric acid, it might make sense to use magnesium nitrate to source magnesium instead of magnesium sulfate.

Sulfur is usually considered the "Freedom" element in nutrient mixes, but I think anywhere over 100ppm S is too high.

Except again i believe magnesium nitrate is kinda expensive. You can make it with .....nitric acid lol. And magnesium but again nitric is expensive and magnesium reacts violently with water.

78% sulfuric acid. I buy mine from an auto parts store, 5 gallons at a time. Cheap, like $16.

I tried buying it around here and they looked at me like I was a terrorist
. Finally got some at the battery store and told them it was for the saltwater aquarium i dont own lol.