Mid-cycle alkalinity settling at 6.3

[eonblue]

This is my first aquarium, and I'm currently 20 days into cycling using Dr. Tim's products. Probably a few days out from finishing.

One thing I've noticed the last couple of weeks is that my alkalinity will always settle at 6.3. I'll add B-Ioniq and see it go up to 7.5, then drop right back to 6.3 in two days and stay there. I know the ammonia eating bacteria will use alkalinity, but I have been at 0 ammonia for a week while waiting for nitrites to process, and still alkalinity will fall shortly after a dose.

My current theory is that the AquaForest stone mix I used on the rocks is pulling carbonate out of the water. Calcium has not dropped, and magnesium went from 1300 to 1240 over 10 days. Any other ideas about what might be causing this pattern?

I know it's not causing any issues, and I don't intend to add corals for a couple of months; it's mostly just curiosity. Also, I'm using Hanna colorimeters for testing.

 

[Fish Fan]

It's normal for Alk to fall during a cycle as the bacteria can consume some of the Alk ions. I wouldn't worry about Alk until you're ready for corals.

And, if your ammonia is zero, you're cycled. The nitrite is non-toxic in saltwater tanks, so there's no need to wait for it to zero out

Good luck with your tank!

 

[eonblue]

Thanks! I'm not worried; it's just weird that it sticks at 6.3. Like whatever is taking alk from the water stops when it gets to 6.3. I'm still learning about the chemistry though, just curious.

 

[bryster]

Thanks! I'm not worried; it's just weird that it sticks at 6.3. Like whatever is taking alk from the water stops when it gets to 6.3. I'm still learning about the chemistry though, just curious.

What's a good number to aim for ?

 

[eonblue]

What's a good number to aim for ?

Ideally around 8 but it's more important to keep it stable when you have coral. My tank is still empty so not worried about big swings. I'm sure once the biome is established I won't see the drastic drop after dosing.

Calcium, Magnesium, and pH all work together with alkalinity in ways I don't understand yet.

 

[Fish Fan]

Calcium, Magnesium, and pH all work together with alkalinity in ways I don't understand yet.

pH is dependant on alkalinity (which is a group of ions) and carbon dioxide in the tank and in the air around the tank.

Alk, Calc, and Mag are the "big three" for coral care, but if like most newer reefers you're planning on keeping easy going soft corals, mushrooms and Zoas, you really don't need to worry much about testing these parameters. Soft corals don't consume these elements nearly as fast as their stoney coral cousins because they are not building a calcium carbonate skeleton. Just by doing regular, partial water changes, you'll keep these parameters well in line for a softy tank, no test kits required

If you do want to did further into the chemistry, this is a pretty good video to start with:


I hope that helps!