Low ALK in new tank

[pned_521]

I set up my 47gal AIO lagoon tank end of Dec ‘25. Dry rock with Oceans Direct sand.
See pic.
I added 400grams Eheim ceramic media to the baffles in the back. I’ve been keeping freshwater tanks for 8yrs and thought more media couldn’t be a bad thing.
I started with saltwater mix from my LFS.
I don’t know the brand they used or the parameters of just the saltwater at that time.
Lesson learned to test it before adding if I buy saltwater again.
Added 2ppm Fritz Ammonia and TurboStart 900.
Nitrogen cycle is complete.
I’ve added 1ppm ammonia 2x to test cycle.
Within 36-48hrs ammonia and nitrites are back to zero.

My Alk has hovered around 6.5-6.8 the entire cycle.
I have a BRS RODI and am using Fritz blue box.
I’ve tested adding 1/2 tsp baking soda mixed in RODI to bring Alk up.
It helped, but after doing some more research I came to conclusion that adding baking soda was for more established tanks.
I’ve done 2 WC’s, first was 20 gal, the second was 10 gal, and I pulled out 1/2 the ceramic media to see if it would help drop my phosphate and nitrate which are both high.
Phosphate swings quite a bit.
Alk raised to 7.2, but has dropped back to 6.5.
I’m using a Hanna checker, I reorder the reagent and have used that a few times thinking it was possibly the reagent.
I’ve also ordered a Salifert kit to check against the Hanna incase the Checker itself is bad.

In the 2 FB groups I’m in, the recommendation is to wait it out and the Alk will increase on its own.. can the dry rock be absorbing Alk?
I have the Tampa Bay Saltwater Jar kit arriving next week to add to the tank.

No livestock or corals at all.
I don’t think the tank is ready to start dosing.
I’ve considered trying a higher Alk salt, but that’s a bit expensive and am thinking this could throw off all my other parameters.

Any thoughts on why the Alk is so low, but generally stable at the level it’s at?
Pics of parameters from last 2 weeks.
I test pretty regularly in hopes of seeing the Alk increase.
Thanks in advance

 

[Fish Fan]

Sorry you're having some difficulty here. First thing I'd ask is did you check the salinity of the saltwater you purchased, and what are you using to check salinity? Has it been correctly calibrated? A lot of times calibration fluid that you buy isn't as spot-on as we'd hope, so it's a very good idea to make your own. You can make your own solution easily with regular Morton's table salt and a decent kitchen gram scale or measuring spoons. This link has more information:
https://www.reef2reef.com/ams/reef-aquarium-salinity-diy-calibration-standards.956/
Good luck!

 

[pned_521]

Sorry you're having some difficulty here. First thing I'd ask is did you check the salinity of the saltwater you purchased, and what are you using to check salinity? Has it been correctly calibrated? A lot of times calibration fluid that you buy isn't as spot-on as we'd hope, so it's a very good idea to make your own. You can make your own solution easily with regular Morton's table salt and a decent kitchen gram scale or measuring spoons. This link has more information:
https://www.reef2reef.com/ams/reef-aquarium-salinity-diy-calibration-standards.956/
Good luck!

Thanks.
I don’t believe I checked the saltwater before I added it to the tank, only after.
I use a Milwaukee salinity checker for speed and accuracy. The speed of the test allows for more frequent testing, which means I’ll do it more frequently.

Considering another larger WC this weekend to see if that helps to dilute the initial water that was added more.

 

[Randy Holmes-Farley Verified Community Expert]

Cycling reduces alk as ammonia is converted into nitrate, and bare calcium carbonate surfaces can be sites for more precipitation until things like bacteria, phosphate, organics, and magnesium clog up the surfaces.

6.5 dKH is not particularly low and is fine until you add corals. At that time, I'd just add a little backing soda. This calculator shows how much:

https://reef.diesyst.com/chemcalc/chem_calc3.html