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Alkalinity and PH


ImGoingCoastal

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Magnesium chloride won't "expire" - other dry goods can sometimes slowly react over the long term and slowly convert to nearly insoluble compounds. But, you're safe with magnesium chloride.

 

When I say low pH, I'm talking about something in the area of 7.7 or lower. Most folks don't have this situation unless they've got a buildup of CO2 in the tank from, say, a calcium reactor. If you have this situation, then the first thing I'd do is double check your test or calibrate your pH meter to make sure that you're getting an accurate assessment of your situation. (There's nothing like being led down a bad path by a bad measurement - and it happens far more often than you might imagine.) If you read the RHF article, you'll see that baking soda (sodium bicarbonate) will slightly and temporarily (Temporarily = less than an hour, typically, in a tank with good aeration) depress pH.  You can mitigate this by dosing (a dissolved solution of) it somewhat slowly. Baking the dry baking soda drives off a CO2 molecule and converts it to sodium carbonate. When sodium carbonate is added (again, dissolved in water), you'll get a sharp upward spike in pH that can be pretty severe if dosed too quickly. Baking soda is normally the more safe alternative.

 

Kalk has a similar effect of sodium carbonate, so it's normally dosed very slowly - using a kalk stirrer - over the course of a day. Kalk is short for kalkwasser, a German word for "limewater"  (which is rich in calcium, kalzium in German). Kalk is calcium hydroxide Ca(OH)2, and doses BOTH calcium and alkalinity at the same time. The problem is, it's nearly insoluble - dissolving very little in water to where a saturated solution of it (without suspended particles, known as kalkwasser, has a very predictable concentration. Kalkwasser, if dosed throughout the day (or dosed only at night in some approaches) as part of your ATO, can help raise pH in your tank. Because of the low saturation level, it's impossible to dose enough kalkwasser to a mature SPS tank through an ATO delivery system because you simply cannot add enough of it. (There are other approaches to this involving manually dosing kalk slurry, but they have signficant drawbacks.) In the past, SPS aquarists went through a progression of techniques to replace calcium and alkalinity in their tanks:

 

water changes ==> kalkwasser ==> calcium reactors or two-part (sometimes supplementing the kalkwasser, sometimes replacing it)

 

Kalkwasser, while a natural "balanced" additive - that is, it delivers calcium and alkalinity in nearly exactly the same proportion needed by corals - has risks associated with its use. Overdosing your tank with kalkwasser can lead to a crisis or disaster. (We have other threads on that here in the forum.) Personally, I still use kalkwasser.

 

Many users today go directly to two-part systems when water changes no longer address consumption. Some go to calcium reactors, but their initial cost and relatively complex setup can discourage this route for many. Manual dosing of two-part becomes tedius very quickly. Most folks want to invest in a three-head peristaltic pump, or "dosing" pump to automate this. Dosing of any sort, though, requires an implicit acknowledgement that TESTING is CRITICAL. "Don't dose if you can't test." After all, you're trying to replace ions that have been consumed. How can you accurately "replace" if you can't measure how much has been used up?

 

There's plenty of stuff out there on how to set up a two-part dosing system, but here's a video from Robert at Marine Depot on how to use Hanna's colorimeter checkers to dial-in a two-part dosing system.

 

 

 

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