A very short explanation of alkalinity and ph

[Sk8r]

"In chemistry, pH (potential of hydrogen) is a numeric scale used to specify the acidity or basicity of an aqueous solution."---wiki. Ie, is your water acidic like lemon juice---or alkaline like a desert pool?
On that scale, battery acid (ph of 1) and drain cleaner (ph of 12)---both extremes can burn.
Your tank should be between 7.9 and 9 for the comfort of fishy skin and gills.

BUT--- ph in a marine tank wanders all over the map during a given day. Pretty well toss your ph meter---it's only going to tell you how it is THIS hour.

SO---in the marine hobby---we track alkalinity.
What is alkalinity?
"Alkalinity refers to the capability of water to neutralize acid."---wiki.
It is essentially its 'buffering' capacity, buffer, as in---to soften...referring to its 'carbonate hardness' or dkh.
Stay with me: this is NOT rocket science: I'll explain.

"Carbonate hardness, or carbonate alkalinity, is a measure of the alkalinity of water [caused by the presence of carbonate (CO2− 3) and bicarbonate (HCO− 3) anions"...but you don't need to know that to use it]. Just say that you want, generally, a dkh of 8.3. It's a nice number. It can be safely as low as 7.9 or as high as 9.

You can test your dkh with an Alkalinity Test. I use Salifert, quickest and dirtiest of all water tests, which is good, because it's the one you should run weekly on ALL KINDS of tanks. [unless you're running kalk, in which case you track your magnesium level, but that's a whole other kettle of fish.]

If your alk is 8.3 or slightly either side of it (7.9 to 9.0) your alk is great, your fish are not swimming either in battery acid or drain cleaner, and that is ALL you need to track because dkh actually measures how able your water is to keep the water safe and comfy. Tracking ph will drive you crazy. Track alk: it's a much more stable number, and SHOULD stay rock-steady. That's your job. To affect alk, you add buffer. Your general danger is water that's too acidic...so you just keep that buffer level right in that ballpark and you are good.

 

[Maggie321]

This was great! I am not a chemist so reading about all this stuff can get confusing. It's great to read it from another perspective, explained another way. Thanks!

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[Apotack]

Check sk8r's other posts, you won't be disappointed.

 

[ReeferNoob4ever]

I like to test for pH cuz it's fast and easy! Plus, mine is either 8.1 or 8.3 and I've found more importantly that seems to directly correlate with the tanks dissolved oxygen level. I look for stable parameters rather than exact numbers. If my tank is the same every time I test it, then I know my practices are in working order. Keep in mind that it mainly depends on how many things in your tank are using up resources such as bicarbonate and calcium. Even algae sometimes.

I'm curious for you to explain mag testing and kalkwasser please. Awesome post!

 

[Sk8r]

IANAC---but magnesium is kind of like a dipstick for stony reef tank chemistry. If you have gotten your tank to the parameters: 8.3 alk, 420 calcium, 1350 magnesium---AND put kalk (powdered lime) in your topoff water---the tank will hold its alk and cal rock-steady as long as the mg stays above 1200 (it gets used up very, very slowly) and as long as the flow of kalk-laced water is uninterrupted. To this end, you 'set' your levels by dosing, then start the kalk-water flow, and test your magnesium weekly. Here's the even cleverer part---if you keep refilling the kalk-water (ro/di with 2 tsp kalk powder per gallon, stirred only once)---and keep dosing the mg when it gets toward that 1200 mark----you can keep this game going on and on and on. My record is 6 months before I goof it up. Six months of total chemical stability is nice!

The only catch is, you need enough evaporation in your tank to drive the ro/di enough---and if your tank is over 75 gallons and stuffed with corals, they'll eat faster than evaporation-driven topoff can provide calcium: at that point you get a calcium reactor. But until that point, at about 2.50 a pound for kalk, you're getting tank stability for very little money. Because it's so simple, I can go on vacation for four weeks and tell a non-reefer tanksitter---just watch the water level in this tub and when it gets low, switch tubs.

[As a side note, this is kind of how the ocean does it: Magnesium is 8th most common mineral in Earth's crust, and is in seawater; the water hovers around 7.9 dkh, and that dissolves old coral, maintaining calcium level. So in the presence of magnesium and at a dkh within the range---the ocean dissolves calcium-containing shells and coral skeleton to feed living coral and fish the calcium they need.]

 

[LuizW13]

Thanks fr the explanation sk8r. I've always been confused by this, always wondered "isn't alk determined by the ph of the liquid?"

My order for most of my aquarium equipment has just been shipped today, oh boy am i excited to get this going!

I only purchased tests for ammonia, nitrate and nitrate though -I suppose i'm okay with with those three for the time being until i get some fish in my aquarium, right? I don't plan on having an SPS corals until i feel comfortable doing water changes, tests, etc.

 

[Maggie321]

IANAC---but magnesium is kind of like a dipstick for stony reef tank chemistry. If you have gotten your tank to the parameters: 8.3 alk, 420 calcium, 1350 magnesium---AND put kalk (powdered lime) in your topoff water---the tank will hold its alk and cal rock-steady as long as the mg stays above 1200 (it gets used up very, very slowly) and as long as the flow of kalk-laced water is uninterrupted. To this end, you 'set' your levels by dosing, then start the kalk-water flow, and test your magnesium weekly. Here's the even cleverer part---if you keep refilling the kalk-water (ro/di with 2 tsp kalk powder per gallon, stirred only once)---and keep dosing the mg when it gets toward that 1200 mark----you can keep this game going on and on and on. My record is 6 months before I goof it up. Six months of total chemical stability is nice!

The only catch is, you need enough evaporation in your tank to drive the ro/di enough---and if your tank is over 75 gallons and stuffed with corals, they'll eat faster than evaporation-driven topoff can provide calcium: at that point you get a calcium reactor. But until that point, at about 2.50 a pound for kalk, you're getting tank stability for very little money. Because it's so simple, I can go on vacation for four weeks and tell a non-reefer tanksitter---just watch the water level in this tub and when it gets low, switch tubs.

[As a side note, this is kind of how the ocean does it: Magnesium is 8th most common mineral in Earth's crust, and is in seawater; the water hovers around 7.9 dkh, and that dissolves old coral, maintaining calcium level. So in the presence of magnesium and at a dkh within the range---the ocean dissolves calcium-containing shells and coral skeleton to feed living coral and fish the calcium they need.]

You say 6 months of total stability, did you do water changes at all? What was in the tank? Just coral or were there fish also?

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[Ron Reefman]

Sk8r, these are two terrific posts. I'm a physics guy and I struggle a lot with chemistry. Back 10-12 years ago when I was learning this (the hard way) nobody ever explained it better than you just did. Clear, just enough chemistry to explain it and not so much as to make it confusing. Excellent job! This should be a 'sticky' for sure.

 

[Sk8r]

Thanks, Ron!

 

[Sk8r]

Maggie, water changes are how you replace your traces (elements). You just suck a few gallons out of the sump and put a few in, which has nothing to do with topoff, really or kalk, except that you DO shut down the topoff for a few minutes! But I don't even have to cut the return pump. By total stability I mean no fuss with the alk-cal-mg triad, which is key to having water your fish will enjoy. The regular water changes are good for the fish, too, and probably more so for the corals.

 

[vashawn]

thanks......