Alkalinity

[Tim]

After spending most of the day fooling with my tank I tested all my levels. Everything looks good except the Alk. I read that acceptable levels are between 8.0 and 13.0. I've tested it twice in the last 2 weeks and the readings were 2.2 and 2.0. Can anyone tell me why it might be so low? And is there anything I can do to get it back into the acceptable range?

 

[little_fish]

I would first double check the reading against another test kit, but it really common for our tanks to have low alk. If you do have low alk I would consider upping your water changes and see if that solves the problem, if not you will need to dose alk. They have liquid supplements you can buy at the LFS, and then you just follow the directions to carefully raise the alk to the correct level and then figure out what the maintenance dose it.

 

[daugherty]

also are you testing DKH or ppm

 

[Tim]

little fish, I've done 20% water changes every week for the last 8 weeks, so I dont think it would be that. The test kit on the other hand maybe, I'm sure the one I have is far from the best and I'm not really sure how old it is, daugherty may have solved the the problem by just getting me to read the box a little closer. According to the box the reading is measured in meq/l, not DKH or ppm. I have no idea what that is but it also says by that measurement the Alk should be maintained at 2.2, which is right where I am. Amazing what reading instructions will do sometimes:) Thanks guys.

 

[ccCapt]

2 meq/l = 100 ppm = 5.6 dKH. That's too low. You want it around 2.8 meq/l - 143 ppm - 8 dKH.

 

[FishyReef]

Glad I read this post - I've been thinking my Alk was too low at around 4 - 4.5, but just re-read my kit instructions and it too is measured in meg/l - so an Alk of 4.5 is in just the right range, yes?

 

[ccCapt]

4.5 meq\l = 12.6 dKH. That's a little high. I keep mine around 8-9 dKH.

Reef Aquarium Water Parameters by Randy Holmes-Farley - Reefkeeping.com
"I suggest that aquarists maintain alkalinity between about 2.5 and 4 meq/L (7-11 dKH, 125-200 ppm CaCO[SIZE=-1]3[/SIZE] equivalents)..."

 

[FishyReef]

Thanks for the link! My first question was going to be how do I lower alk.... but in reading through the info on the link, I came across this:

In normal seawater or marine aquarium water, the bicarbonate greatly dominates all other ions that contribute to alkalinity, so knowing the amount of H[SIZE=-1]+[/SIZE] needed to reduce the pH to 4.5 is akin to knowing how much bicarbonate is present. Aquarists have therefore found it convenient to use alkalinity as a surrogate measure for bicarbonate.

One important caveat to this surrogate measure is that some artificial seawater mixes, such as Seachem salt, contain elevated concentrations of borate. While borate is natural at low levels, and does contribute to pH stability, too much interferes with the normal relationship between bicarbonate and alkalinity, and aquaria using those mixes must take this difference into account when determining the appropriate alkalinity level.

I am in fact using Seachem salt mix, which leads to a different question of whether my alk is in fact okay at 4.5 meq/l?

 

[ccCapt]

The only way really to lower alk is water changes with a salt that has a lower alk level. Or...let it drop naturally. Calcification (hard corals growing and coralline algae growing) will help drop it.
I believe that since that article was published (and because of that article), Seachem changed it's formula and lowered the borate concentrations.