ph drop

[digitalsteve]

hey guys , i was wondering how you drop the overall ph of your tank, i have a buffer but i am afraid that it will raise it , is there a secret to dropping it?

steve

[digitalsteve]

bump

[bear27]

In the past I have used small amounts of viniger to drop my ph but this is a temporary fix you need to get your buffer up to keep your ph stable

[Delphinus]

I'm kind of curious why you'd want to lower your pH? What's it at right now? Generally you don't need to mess with pH, and usually if you have anything going on that affects pH, you'd want to attack the cause and not the symptoms.

[Rikko]

Baking soda. The chemistry behind it boggles me (NaCO2 will bring your pH to around 8.0 and will boost your alkalinity... Higher alk means a drop in pH is resisted.. So how does that work?), but I've heard of many RC people using it.
Muriatic acid is another common chemical used. Personally I'd just let it be. Without your rock to buffer it, your pH would plummet to 5ish on its own.. It should plummet in time to the pH that the rock buffers to anyways.

[Aquattro]

Originally Posted by Rikko

Without your rock to buffer it, your pH would plummet to 5ish on its own.. It should plummet in time to the pH that the rock buffers to anyways.

Excuse me??? It most certainly would not plummet to 5ish, and rock does not, to any appreciable amount, buffer salt water.
You may see a drop to high 7s, with a large acid content (from ammonia byproducts) at which point aragonite may start to dissolve( I think the actual value is around pH 7.6 where aragonite starts to dissolve) and this in turn may act as a buffering agent to prevent it from going lower. Most tanks that experience regular partial water changes would not get to this point though.
As proof, my 25g tub that has my new water is at pH 8.1. After more than amonth of sitting in the tub, the water is still 8.1, no rock , no nothin'. It does not plummet to pH 5.

[Rikko]

<shrug> I've seen FW Tanks in the high 5s. I would assume with no carbonate solids in the water dissolving (ie. no substrate, no calcerous rock of any description) it would behave much the same way for salt. It's not very bloody likely to happen, but I'd be willing to put a small bet that if you hooked up a HOB filter to a small tank of saltwater and just slowly fed it ammonia to see how far the bacteria could take it, that it would drop rather horrifyingly low. (Bad, bad, bad sentence) Alas I lack the dedication to run such an experiment for the weeks it would take. But I don't claim any reef tank can ever get that low - only that a tank with 0dKH can rocket down there pretty sharply.
Rock most certainly buffers the water.. With a ton of live rock and a sand bed, admittedly, still not enough to compensate for what corals suck out, but it's definitely happening.

An intellectual exercise; certainly not a realistic illustration.

[Aquattro]

Yes, a volume of salt water, when depleted of alkalinity AND fed a source of acid would theoretically go very low on the pH scale. However, this same volume with an aragonite substrate would still go that low, albeit at a much slower rate.
The rock would act as a buffer as the pH got low enough to initiate dissolution of the CaCO3, but again, the alkalinity would eventually deplete, removing any buffering capacity.
Also, keep in mind that rock and gravel will contribute to this in very different ways based on available surface area. The amount of exposed rock surface is minimal compared to the surface in a sandbed.
Remeber though, that aragonite doesn't dissolve at pH at normal seawater levels.
In theory though, yes, you're experiment would work. I think.

[Rikko]

I guess (getting way off topic here), that that's also the reason we use calcium hydroxide or calcium chloride to buffer our calcium levels, isn't it? Calcium carbonate, while giving us exactly what we want (a 2-part additive in one, say), dissolves so bloody poorly that it wouldn't get us very far.
Might also explain why mixing calcium carbonate, sodium bicarbonate, and water in the same vessel doesn't help either. From what I gather, combining your additives together lets you precipitate calcium carbonate, heats the whole mess up, and foams like hell. It was actually rather fun to watch.

Er, and that tank I've seen firsthand with a 5s pH? That was my first freshwater tank, before I'd heard of pH.

[StirCrazy]

Originally Posted by Rikko

Er, and that tank I've seen firsthand with a 5s pH? That was my first freshwater tank, before I'd heard of pH.

with fresh water it is a different animal, especial since we have such soft water out here to start with. as the poop and everything breaks down it causes acids that bind and neutralize what little bufferers we do have in the water and drop the PH. take the starting point of my water, 17ppm and a PH of 6.4 and it will stabilize at a PH of 5.8. we do not add anything specifically in a fresh water tank to stop this like we do in a salt water tank. no water changes that really replenish the buffer, no Ca reactors to fix it.. ect..

Steve