How to use acid for alk.

[Wildreefs]

I expect it is fine. Most that I googled are polystyrene which is fine.

Thank you. I did use it, left in syringe for maybe 5 minutes or so, didn’t melt or corode the plastic at all. Guess it is ok lol.

And lastly, how is acid different then hydrogen peroxide, in a sense where the peroxide when dosed in tank, is away from live stock and will oxidize where it hits.

For example, if you want to hit hair algae, putting a few mls in the sump is not as effective as just squirting it into the algae.

But the acid, when dosed in a body of water, lowers the total alkalinity , not just the the few gallons it immediately hits.

I guess what I’m asking is, how does the acid evenly lower alk in the body of water, but peroxide only works in general area where it is dosed?

Hope that makes sense , I can visualize what I’m trying to ask, but not actually condense it in a sentence lol

 

[Randy Holmes-Farley Verified Community Expert]

Acid converts the bicarbonate in the water to CO2 and carbonate to bicarbonate. Both of those things lower alkalinity, and as it mixes in more, you are just mixing low alk and high alk water to get medium alk water.

Peroxide can have a number of effects, some of which will last longer than others, but the peroxide breaks down to O2 and water, which had no lasting effects.

 

[Wildreefs]

Ok, so I understand, in summation, I’ll give. A crazy, non realistic example.

If I mix new saltwater in a column tank, say 50 gallons saltwater, in a container that’s 15 feet tall, 8 inches wide. If I place 75 ml of muriatic acid in the top of tank (1.5 ml to 10 gallons saltwater to lower 1dkh) then the alk even at bottom, 26!feet away from where I dosed it, will end up with same alkalinity as the top. Even if it takes a few minutes for that acid to circulate down there?

 

[Wildreefs]

Like I can shoot the 2 ml in one spot in my 10 gallons of new water, not spread it around in different places to evenly distribute it.

 

[Randy Holmes-Farley Verified Community Expert]

Ok, so I understand, in summation, I’ll give. A crazy, non realistic example.

If I mix new saltwater in a column tank, say 50 gallons saltwater, in a container that’s 15 feet tall, 8 inches wide. If I place 75 ml of muriatic acid in the top of tank (1.5 ml to 10 gallons saltwater to lower 1dkh) then the alk even at bottom, 26!feet away from where I dosed it, will end up with same alkalinity as the top. Even if it takes a few minutes for that acid to circulate down there?

Correct. A tank with different locations of different alk (by simply adding fresh water, for example) rapidly equilibrates so the whole tank system has the same alkalinity.

 

[Randy Holmes-Farley Verified Community Expert]

Like I can shoot the 2 ml in one spot in my 10 gallons of new water, not spread it around in different places to evenly distribute it.

Bad plan, but yes. The very low alk and pH may damage organisms before it mixes in. I personally would not add acid to a reef tank unless it is done extremely slowly. It is a better plan for new salt water.

 

[Wildreefs]

Oh no no. This would only be in a separate vat, to make new saltwater, no living organisms in there , and then aerated for 8 hours or more before going into a tank with livestock

 

[Dkeller_nc]

By the way - the amount of concentrated hydrochloric acid that must be added to a given quantity of seawater at a particular specific gravity and alkalinity to lower the alkalinity by a specific amount can be precisely calculated. It's a straightforward stoichiometric ratio (i.e., the reaction of HCl and carbonate/bicarbonate goes to completion).

Chemistry jargon aside, what I'm getting at is that if you make the same amount of seawater up to the same specific gravity every time, and the manufacturer provides a seawater mix that contains a consistent amount of alkalinity components, the total amount of HCl that you need to add to reach your desired alkalinity end point will be the same every time. So if you go to the trouble of measuring exactly how much HCl you're adding as you're adjusting the batch, subsequent batches will need that same amount.

Edit: I now see that Landlubber gave you a formula for calculating how much to add in post #5. That could be derived/checked with a table for the density of 12N HCl, but I'm afraid it's a bit too early and haven't had enough coffee for me to do calculations (even simple ones). But you can simply use the formula as a starting point, keep up with the amount of acid you're adding to the container, and test to verify your target alkalinity. Then simply repeat that amount the next time - you should get equivalent results.

You asked about the grade/source for concentrated hydrochloric acid (often sold as "muriatic acid"). The pool supply companies would be my recommendation as a balance of purity, availability, and cost. I would not recommend muriatic acid sold for the purpose of etching concrete (at a home store). Concentrated mineral acids in general are subject to metal contamination in the cheaper grades. Often, that contamination is iron, which is irrelevant for our purposes. Nevertheless, I'd personally be sourcing the pool grade material if you're going to be doing this on a regular basis.