Where’s my alk going?

[Gho5t]

I have a 80g cube, 100g total water volume with sump and I’m dosing B-ionic 2 part at a rate of 150ml a day and I’m still dropping 1dKh / day. The tank is 7 years old, has coralline covering 2 walls but no corals at this time. 150ml seems excessive for a 100g system and I’m hesitant to just keep pumping up the dosage. When I did have corals I was only dosing 40ml a day and maintaining my KH around 9. I’m not seeing precipitation on heaters / pump or a hard sand bed. Any ideas on why the tank would have such high Alk demands and should I just keep pumping up the dosage till it stabilizes? At this point I’m just trying to maintain 8.5.

 

[T-J]

The first thing I would do is verify my levels with another test. How are you testing Alk?
Can you buy a different brand test kit, or go to your LFS for testing?
Having said that, I do know that coralline can be an alk/calc sink.

 

[Gho5t]

Thanks for the reply. I have a newly setup Apex Trident... about 2 weeks old, but I’m also verifying the alk results with Hanna and RedSea test kits. All are within the range of tolerance so the readings appear accurate. Also when I raise levels manually using Seachem Reef Buffer it does adjust to the expected value so the values, other than the consumption rate do seem to make sense.

One thing I noticed last night was a build up on the wall of the sump where the dosing lines feed. It looks like maybe it was splashing the additive and not all going into the tank. I put a small hard plastic tube on the end of the return line and adjusted the drip location to make sure it was falling straight down into the sump. This morning the Alk rose .3 over 6 hours. That’s the first I’ve seen it rise, so maybe it was a mechanical issue more than anything.

If that shift holds true then I could lower the dosage by ~40ml putting me in the 110ml/day range. Still seems a little high but I think I’d have to chalk that up to the coralline. It’s pretty dense and up to a 1/4” think in places.

 

[Bayareareefer18]

Possibly low mag, causing precipitation ?

 

[1guydude]

How long are your lights on?
Id say scrape that purple coraline depending on how thick it is.
Cpl small wcs and give it a day. Than go back to testing and dosing accordingly.
Hths
D

 

[Gho5t]

Possibly low mag, causing precipitation ?

Mag is solid at 1360... I finally got it to stabilize at 150ml/day holding 8.3dKH. I’m guessing at this point it’s got to be the coralline.

 

[Gho5t]

How long are your lights on?
Id say scrape that purple coraline depending on how thick it is.
Cpl small wcs and give it a day. Than go back to testing and dosing accordingly.
Hths
D

Lights are on for 10hours with a 1hr ramp up/down. Just upgraded to a Radion XR30 Blue so that’s definitely a variable. I think you’re right about scraping the coralline. At this point I think it’s the only reason for the uptake.

I was able to get it to stabilize at 150ml/day though so at least I don’t feel like it’s falling into an endless pit anymore.

 

[Randy Holmes-Farley Verified Community Expert]

You are dosing about 3 dKH per day (assuming you are using the proper solution).

Coralline alone in a soft coral tank can use 2 dKH so it may not be excessive, but it might be.

I'd personally let the alk fall to 7 dKH (higher alk means higher demand), and consider switching to baking soda instead of the soda ash to let the pH drop a bit. Those two things will reduce abiotic preciptitation that you may not see.