Alk wont go down


New member
Hey RC, I've been in this hobby since '01. Like many, I've left and came back several times. Had small (10g & 15g) to medium (60g, 100g) to large (190g) systems, so I do have some experience. I just can't seem to figure out why my Alk won't go lower than 10dkh. Consistently between 10-12dkh (stopped 2-part in hopes to bring down Alk).

Some background; I'm currently running a 26g system that's approx. 1.5yrs old. SPS dominant with a few zoas and LPS along with a 6" deresa clam. Everything is healthy, color is great. Growth is okay; encrusts at the base with some growth on tips.

I had been running ULNS by accident dosing vodka and running GFO, activated carbon along with a skimmer. PO4 and NO3 were undetectable which caused all my SPS to look pale. Currently however I've stopped dosing vodka, removed the GFO, carbon and have been feeding more liberally and colors have came back. I do 10% water changes weekly. My tank is in my formal room surrounded by windows which I open daily and Alk still remains currently at 10dkh.

I test with Hanna and Salifert. My current params:
Ca: 380
Alk: 12
Mg: 1400
PO4: 0.00-0.03 (Hanna low range)
NO3: 0-2.5

My dosing includes:
Bionic 2-part (stopped for the past week to try and bring Alk down)
1.5ml AcroPower (daily)
1 drop Lugols Iodine (weekly)
Phyto Plankton (2x week)
Zoo Plankton (2x week)

Coralife Marine

I typically prefer to keep the big three at 400-420, 6-7 & 1400. I know better than to chase numbers but I still feel like my Alk is a bit high and needs to come down some. At this point, I'm assuming the culprit to be the salt mix. Although I've stopped dosing 2-part, my Alk remains at 10dkh and jumps to approx 12dkh after water changes.

I've considered adding kalk to my ATO to balance out PH in hopes to bring down Alk. I also plan to switch to TM Pro Reef salt.

Please feel free to chime in. If anyone has had similar issues, please share what you've done to resolve the issue. TIA


New member
I was thinking the salt myself, maybe mix a batch let it sit a day with a powerhead on it then check ALK to see where you stand with that brand?
Im using IO Reef Crystals & im at the opposite end i have to dose or my ALK drops to 6 so i dose to bring it to 8.
Anyway its where id start. :)


Premium Member
How long has it been since you stopped carbon dosoing and removed the GFO? WHen corals are bleached or partially bleached for whatever reason it can take weeks to months for them to recover. If you're only getting minimal growth and it's only been a couple weeks since you've started raising PO4 I wouldn't change anything you're doing now and be patient for a month or more before making any changes to give your corals time to recover.


New member
It has been approx 3 weeks since I've removed GFO and activated carbon. I haven't dosed vodka for well over 3-4 months now. My corals are no longer pale and have regained some color. Polyp extension is good. Just super slow on growth rate.

If I raise calcium at a moderate rate using a calcium additive, this should drop alkalinity (moderately) as well, correct?


New member

The issue here is that my Salifert test kit went bad. I was down to the last 3-4 tests so I purchased a new test kit from the LFS. I tested my water using both the old and new Salifert kits and the old one was inconsistent. Returned several Alk results of 15+ without dosing 2 part for the past week or so. At one point, the water would no longer transition from blue to pink!

Tested with the new kit and readings came back consistently at 5, which makes sense because my Ca results are low as well coming back at 360-380. Surprisingly, my Mg remained at 1380-1400, which I also stopped dosing for the past week or so.

Going to slowly raise Ca and Alk throughout the next couple of weeks. I'm just glad I found the issue and none of my corals were compromised!