I AM IN NO SUGGESTING OR RECOMMENDING THIS TO ANYONE!
This is in response to a question asked in another thread, people are curious why folks have so much difficulty altering the pH of their water with acid.
Indeed it is Alkalinity of which carbonate hardness KH, is a subset that resists (buffers) acid lowering pH.
Poor man’s alternative to RO as well as maintaining the general hardness (GH).
- When sufficient acid “overcomes” the KH, the pH drops.
- The problem is that unless the carbonate is actually removed the “buffering” will return and the pH will return to its previous value.
First is liming, many of us have seen this when dosing fertz containing Calcium, in fact it is the one point where KH and GH actually cross.
I have read many times about people saying it “snows” when they dose fertz. I resist saying anything as many “experts” like more complicated answers.
It is really Calcium bonding with the carbonate and precipitating, usually Calcium carbonate.
- Effectively reducing the KH and not adding to the general hardness.
- Industry uses this method to protect equipment, the
- Calcium carbonate settles or is filtered out.
- It is not difficult to reduce the KH in tap water using lime and maybe some heat.
The second method that I really do not recommend, but use myself,
Muriatic acid, HCl.
Follow all the safety rules, serious do this out of doors, in a well-ventilated area, breeze blowing away from you. Use gloves, safety goggles, away from kids, pets so on. If you are a kid, get parental permission and supervision. The stuff can ruin your day (and life)!
I really recommend either being able to determine carbonate hardness accurately either by titration (some idea of chemistry) or a Lamotte test kit, still titration but the stuff is worked out for you. Be careful of even Hach’s and others have end points above pH 5. Make sure you have a reasonably accurate method of measuring pH.
The problem of pH returning, actually it is the carbonates reforming as with the liming above, we removed the carbonates from solution.
In this case we are going to drive the CO2 off the carbonate, effectively removing the carbonate from solution by aeration.
I would never dose Muriatic acid, HCl into my tanks directly, my critters are to curious and even well diluted I would fear the potential damage, damage that might not be immediately apparent.
Which brings the issue of pH swings, if your tank has critters, keep the
- pH changes to no more than pH 0.3 per day.
- In fact if you are changing the pH more than 1 whole point,
- remember that a full point lower is 10 times more acidic
- allow a couple days between the 0.3 drops in pH,
- Fish can be harmed and you may not see the results of the harm for a couple of weeks.
Large changes in pH can irreversibly harm fish,
- the classic example are Neon tetras experiencing a full pH point swing,
- even if the water is immediately stabilized and the fish keeper thinks he got away with it,
- they all look fine, swimming around, eating but two-weeks later the tetras begin dying off and
- within 3-days, a week, they are all dead.
For this procedure I recommend using a tub, garbage can (preferably new, at least clean
), it is nice to have an air pump, capable of really getting the water frothing, moving. Glass air diffusers are better than stone or wood for this (my opinion anyway).
Determine how many dKH you wish to remove, frankly in my tub I usually aim for 1-dKH, figuring I will mix tap water to get the desired d-KH. Honestly there are situations to go under 4-dKH. Generally too much KH is not a problem, there are definite exceptions though.
Now, I have certainly learned that any mention of “moles” of something, “specific gravity,” “normalizing,” “molarity,” and so forth are a big turn off. So I am ripping off Dr. Randy Holmes-Farley.
Dr. Randy Holmes-Farley’s method seems awkward, but I get it. He uses Muriatic acid, HCl straight out of the bottle and refers to it as 11,000 meq/L, so he is seems to be asserting normal Muriatic acid is the 32%, 20-Baumé variety.
Muriatic acid is sold in varying concentrations so adjust accordingly.
Thinking of “acidity as negative Alkalinity” and since 1-meq/L will drop the KH 2.8-dKH
Figuring the water out of my tap is 12-dKH and
- I wish to drop it to say 4-dKH, means
- 12=dKH – 4-dKH = 8-dKH.
- That is I want to reduce 8-dKH, or
- 8-dKH ÷ 2.8 meq/dKH = 2.9 and
- I operate in 20-gallon batches (my preference)
- (1-dKH/11,000-meq) × (1-meq Muriatic acid) × (2.9-dKH) × (3.8-L/1-gal) × 20-gal × (1000-ml/1-L)
- = (1 ÷ 11,000) × (2.9 Muriatic acid) × (3.8) × 20 × 1000-ml
- = 20-ml Muriatic acid
- Add about half, 10-ml Muriatic acid in this case.
- Aerate for a while, check the pH to see if it looks right.
- Assuming things seem correct
- add the remaining 10-ml Muriatic acid
- continue aerating until you have blown off the CO2
- once the pH has stabilized
- (remember it will be rising as the CO2 dissipates)
- change out enough water to lower the pH 0.3
It is actually less complicated than it sounds.