How do I increase alkalinity in my freshwater aquarium on the cheap?

February 5, 2008 6:04 PM

How do I add alkalinity (i.e., buffering capacity) to my 6 gal. freshwater aquarium using something cheap, like baking soda?

I have a small 6 gallon aquarium with four tetras. It's been running for about two months now, and the nitrogen cycle seems to have pretty much run its course. I saw a spike in ammonia, then a spike in nitrites, and now those are both near zero.

But my problem is persistently low pH levels - like near or even below 6.0. I cannot get them to rise, even with regular water changes. The test strip I use indicates that the alkalinity of the water is at the very lowest level, suggesting that there's no buffering available. Frankly, I don't understand why my water changes haven't made a difference - supposedly my tap water (treated to remove chlorine and chloromine) is slightly on the hard side, and my understanding is that regular water changes with tap water should be all that I need to keep the alkalinity at desired levels to prevent sudden severe pH drops.

Anyway, for whatever reason that doesn't seem to be working, and the fish don't seem happy. Can I put a tiny amount of baking soda (or some other cheap substance) into the water to give me the buffering capacity that I lack? I'd prefer a solution like this than buying a commercial product, but I'll do that if necessary.

posted by chinston to pets & animals (12 comments total)

You could try to use calcium hydroxide or calcium carbonate (lime) to increase the alkalinity. This isn't necessarily going to increase the buffering capacity of your aquarium which is a measure of how difficult it is to change the pH of the aquarium (whether it is acidic or alkaline).
posted by peacheater at 6:15 PM on February 5, 2008

Does your tank have a cover? And how well is the room ventilated? Not a fish person myself, but I do water chemistry for a nuclear propulsion plant. We sometimes have pH problems in our water samples due to high atmospheric CO2 adsorbing into the samples. This creates carbonic acid in the water and depresses the pH. It happens even in (or especially in) very pure water.

Maybe that random trivia is useful in some way.
posted by ctmf at 6:25 PM on February 5, 2008

What kind of tetra are in the tank? Is the tank planted? I wouldn't worry about about pH too much. Many tetras come from regions in South America where the water flows through decaying plant matter which increases the softness and decreases the pH.

I would record the pH over the course of two weeks (you shouldn't have to change the water more than that) to see if it stabilizes. I would also make sure that the water surface is agitated the by the filter (i.e. it should sound like a waterfall) this will help to release CO2 from the H20. If your aesthetic can handle it I would suggest a live plant or two to further remove the CO2. I think that it is better for the tank to reach a stable, natural, equilibrium than use water additives to reach optimal conditions. Adding a pH buffer is a band-aid that fixes the symptoms but doesn't eliminate the underlying problem of too much CO2 in the tank.
posted by kscottz at 7:43 PM on February 5, 2008 [1 favorite]

Thanks. There's one serpae tetra and three neons. There aren't any plants or organic material of any kind - just a couple of plastic plants and gravel.
posted by chinston at 7:48 PM on February 5, 2008

How about putting a layer of peat in the bottom. Tetras like high pH iirc, and peaty water suits them. Peat can be had from a garden store. You can bake it in the oven to sterilize it before putting it in the tank.
posted by anadem at 7:55 PM on February 5, 2008

I agree with kscottz that many tetras can handle a low pH. The only problem is that at about 5.5, your biological filtration will cease, and you'll have ammonia start to build up. In turn, this isn't much of a problem at a pH of 5.5, as most of the ammonia is of a non-toxic form at that point. Unfortunately, the first time you do a water change with water at a higher pH, the remaining ammonia in the water changes to a toxic form very quickly.

Agitating the surface is good -- either with the filter, or perhaps even with a small airstone. If the issue is CO2 build-up, this should raise the pH. If it doesn't, you're going to want to buffer up the alkalinity of your water.

The simplest way, if your tetras are a species that can handle a pH of around 7.6 - 7.8 (a bit on the alkaline side) is to add a small bit of calcareous rock or gravel to the tank -- like the "crushed coral" that used to be commonly used in marine tanks. In a freshwater tank, this will establish a fairly reliable slightly alkaline pH (it's a trick many cichlid keepers have used for years).

If your tetras won't do well at that high of a pH, you can try to raise the alkalinity with sodium bicarbonate (baking soda). Try adding a very small amount of baking soda (perhaps 1/2 tsp per gallon) to your new water at your next water change. Test the pH over the next few days (it will fluctuate some after the baking soda is added), and increase (or decrease) as necessary on successive water changes until you achieve your target value, and then do water changes (with the buffered water) often enough to keep it at that level.

The three things you want to shoot for are a) keep the pH above 6 or so (your biofilter will continue to drive it down if there is no buffering capacity (alkalinity) in the water), b) keep it stable, and c) make changes very slowly. Rapidly fluctuating pH is much worse than having it stable at a slightly less than optimal value.
posted by nonliteral at 8:03 PM on February 5, 2008

No, kscottz is right, Tetras generally prefer low pH of ~ 6.5 (they're a South American / Amazonian fish from waters full of tannic acid, etc). Having said that, aquarium trade ones seem to be pretty tolerant of anything you throw at them, although they won't do really well in alkaline water.

If the nitrogen cycle has run its course, then now's the time to let the tank settle and find a good equilibrium. If you're really worried about pH, try introducing some plants to help raise it by soaking up some of the CO2. I wouldn't be overly concerned, unless you're really wanting to keep things with exotic requirements (not likely in a small tank like that) - you're best off letting it find its own status and choosing fish accordingly.

Oh, and pH - like hardness - is due to and affected by a whole lot of environmental factors (e.g. Ca hardness affect/effects pH a lot more than Mg or other mineral hardness). Trying to keep pH, hardness, etc to particular levels purely by chemical addition is imho something of a fruitless exercise - you'll forever be battling what the tank wants to do naturally. Expensive, pointless, and not recommended unless, like I said, you're trying to keep/breed picky species like Discus etc.

You're on the right track though - it's the sudden changes that cause problems. If the tank wants to sit low, don't worry too much about its buffering capacity - just stick to South American and most Asian species. If anything is going to cause rapid changes, there won't be too much you can do about it with such a small water volume...
posted by Pinback at 8:21 PM on February 5, 2008 [1 favorite]

On preview posting: nonliteral is right about the effect of pH on biological filtering, and the addition of calciferous material to raise/buffer the pH. It's just that personally I (a) wonder how much bio-filtering capacity there really is in such a small volume of substrate / filter (unless you've got a large external biofilter), and (b) the point of going too far overboard trying to maintain a situation the tank dynamics really don't want to keep.

Horses for courses though - one thing aquarium practices are guaranteed to do is cause "spirited discussions" (i.e. arguments ;-) amongst aquarists! I figure a lot of it comes down to how much work you want to do, and how much you want to worry endlessly about it ;-)
posted by Pinback at 8:30 PM on February 5, 2008

Final thought, I promise...

If your tetras aren't happy, it's more than likely because you've got 4 of them in a bare tank. They're a schooling fish, and really like lots of leafy shadowy places to hide in if they're to feel at all comfortable. Counter-intuitively, they'll be more active and visible if you've got a dozen or so in a heavily-planted tank.
posted by Pinback at 8:43 PM on February 5, 2008

Pinback's last comment probably has the answer - tetras do best in a crowd of their own kind, and you've got one orphan serpae and three lonesome neons. The serpae probably needs to be upgraded to a larger tank with a school of his own; you might be able to fit a small school (like six) neons in a six gallon tank, but I'm not really a tetra person. (See username.)

Tangentially related question about aforementioned band-aids: what the heck is in those commercially sold pH buffers, anyway? I'm thinking about getting rid of the buffer first recommended to me when I was a wee newbie all of ... last March ... but I can't find an ingredients list for Bullseye pH regulator, and thus I have no idea how it actually affects the tank system.

(I will say, though, chinston, that it does work very well for its purpose. I'd just be happier if I knew how on earth it was doing it and whether I really needed it.)
posted by bettafish at 9:14 PM on February 5, 2008

I (a) wonder how much bio-filtering capacity there really is in such a small volume of substrate / filter (unless you've got a large external biofilter)

If he saw ammonia and then nitrites rise and fall, then there's enough capacity -- at least for the current bioload (all bets are off as the fish grow, of course).
posted by nonliteral at 11:11 PM on February 5, 2008

Just be sure that if you plant your tank, you remove decaying plant material right away, because that will lower the pH as organic acids leach into the water. It's also going to be very important to have good lighting- plants need the light in order to use up the CO2 as they photosynthesize. My congo and bleeding heart tetras are really happy in their heavily planted tank.
posted by oneirodynia at 7:54 PM on February 6, 2008