Spike in Alk?

Kenmx10 · Aug 13, 2015

I've recently set up a frag tang (40breeder w/40 gallon sump). Its been up and running for about 6 weeks. The 1st two weeks it ran with only water. After that I added Fiji Pink sand. At week 4, I added Pukani rock( about 40lbs), and its been running for 2 weeks with the rock. Ive used IO salt and everything tested ok. A few days ago I came home and the tank looked cloud. Almost like white smoke. The next day it was really cloud. I assumed it was a bacterial bloom. I did a 15 gallon water change and the very next day the water was as clear as can be. I checked my parameters while the water was cloudy, and my Alk was over 14. Three days later the water is still clear, but the Alk is still reading over 14. I am using a Red Sea test kit, and it tops out at 14. Calcium is at 425, and Mag tested around 1320. PO4 at 0.16 and dropping, using GFO.

I live on a salt water river, so when I purchased the Pukani, I put it in the water for 4 month to try and eliminate PO4. When I pulled it out, it had some brown soot and green algae on it, so I dosed it in 5% vinegar bath undiluted for 24 hours. Then hosed it off with well water, and soaked it in RO water for 24 hours. Could this be related?

Im wondering if this was precipitation or a bacterial bloom. And why the Alk jumped from around 9 to over 14 and holding. Any ideas? Thx

hybridazn · Aug 13, 2015

Have you tested using another test kit? Its possible that your kit went bad. Another reason xould be your salt just having inconsistencies. Do you mix the salt mix after you buy it to ensure consistency?

Randy Holmes-Farley · Aug 13, 2015

Have you measured nitrate?

If there was a lot of nitrate in the water and bacteria consumed it, that can boost alkalinity.

Consuming 62 ppm of nitrate will boost alk by about 1 meq/L (2.8 dKH).

Kenmx10 · Aug 13, 2015

Nitrate has read zero from day one. But Im questioning my Nitrate kit. Its a Red Sea, and it shows zero to be a light pink color, and anything above that gets darker. Mine has been clear with no signs of a slight pink tint at all. Checked my Alk today and it appears to be about 15.5. Im still baffled how it could jump from 9 to over 15 without dosing anything. The only thing I can think of is, maybe there was some vinegar that was trapped inside the hollow parts of the Pukani thats seeping out. Or possibly the vinegar has softened the rock and maybe some of the rock is breaking down in the water column. Could either of these cause the Alk to jump that high.

Randy Holmes-Farley · Aug 13, 2015

Vinegar won't boost alkalinity, but I suppose if it is dissolving the inside of rock it would (or just that the rock is releasing some from pores that already dissolved earlier).

Could be the alk test kit.

Maybe try it on some new salt water.

Kenmx10 · Aug 13, 2015

Thx Randy, Ill mix up a batch of new water and check the Alk kit. After the vinegar bath the rock did have a significant amount of surface breakdown. It felt chalky, and would rub of real easy. It also clouded up the water pretty good when I rinsed it. I was thinking that, if the rock was still breaking down it would have more of an effect on the calcium than the Alk. But Im not sure what the rock is made of. Or the chemical process of how it breaks down. I might cut a piece of rock in half just to see what it looks like on the inside.

Kenmx10 · Aug 14, 2015

I mixed up a new bucket of salt water and the Alk measured at 8.7 so the test kit seems to be ok. I did look at some rock that is still out of the water, and it has a chalky substance all over it that wipes off as you touch it. Im guessing this dissolved particles from the rock is mixing in the water column causing the Alk to spike. Does that sound possible. If so, I would have though that it would of had an effect on the calcium.

Randy Holmes-Farley · Aug 16, 2015

If there are particulates in the water from pulverized rock, it will lead to a false high reading because the fine calcium carbonate won't dissolve in the tank, but will dissolve in an alk test and appear to be alkalinity when it is not.

Semper.Reefing · Jun 12, 2024

Randy Holmes-Farley said:
If there are particulates in the water from pulverized rock, it will lead to a false high reading because the fine calcium carbonate won't dissolve in the tank, but will dissolve in an alk test and appear to be alkalinity when it is not.

I feel like this just happened to me. Had a spike from 8 to 11.17 per my trident. Only changes I’ve made is dosing 50ml of vinegar to my 250g. I freaked out but everything looks fine in the tank. My Hanna checked read 8.5. Guess I might need to get some re calibration fluid for the trident