What would cause alkalinity to rise without dosing?

[monicalooze]

Since I started testing alkalinity, I have noticed that throughout the week, my alkalinity rises about 1 point. For example, this week it started at 9.4dkh right after the water change, and by the end of the week it was 10.3dkh (before the water change). I do not dose anything and I do not have coral in the tank yet. What would cause this?

And for that matter, why would my alkalinity be 9.4 to start with, when the salt mixes to about 7.0-7.5?

My tank:
10g waterbox cube
Tropic Marin pro salt
RODI
Carib sea live sand
Real reef rock (man made)
Filter pad
Carbon
Ceramic bioballs
1 gal AIO refugium with Pom Pom algae
Running for approx 8 weeks
Weekly 25% water change

Livestock:
1 juvenile ocellaris
1 tail spot blenny
1 scarlet skunk cleaner shrimp
1 porcelain crab
A handful of snails

Feeding (alternating):
LRS reef frenzy
Spiraling brine shrimp
TDO pellets
Algae wafers
Phyto

Current Parameters:
Salinity 34.9ppt
Temp: 24.9 C
Ph: 7.9
Alk: 10.3dkh
Phos: .15ppm
Nitrate: 2ppm

 

[monicalooze]

I should add that I also have a barnacle cluster for the blenny.

 

[dzeleski]

What test kit are you using? Are you following the test procedure as perfectly as possible? Are the test tubes/equipment being cleaned before and after each test?

Are you able to test Calcium and Mag?

 

[monicalooze]

I use the Red Sea test kit for nitrate. The rest are Hanna Checkers. I measure the volume of the water with a syringe and make sure to measure below the meniscus. I wipe down all the vials to make sure there are no finger prints and I make sure there are no bubbles. I clean them with RODI after each use. I'm not sure what else I could do to improve the procedure.

I have a calcium checker, but I haven't tested it yet. I don't have a mag checker. Can those affect alkalinity? How all of these interact is still somewhat opaque to me....

 

[dzeleski]

Its possible you have precipitation going on, if calc and alk are out of balance and mag is low you can have weird test results. Are you testing at the same time every day or at different times? If different times test every day for one week at a specific time. If you are testing at different times you may get different results. If you have sand and poke it with something does it feel hard or is it still soft?

I would check calcium. If it is the hanna calc checker make sure you use either the hanna branded distilled water or CVS brand distilled otherwise you may get an inflated result if your RO water as calc in it (mine does).

If you plan on getting corals def pick up a mag test kit, I personally like the aquaforest kit and BRS has a good video on the best mag testers its the one they like best as well.

 

[NeonRabbit221B]

I use the Red Sea test kit for nitrate. The rest are Hanna Checkers. I measure the volume of the water with a syringe and make sure to measure below the meniscus. I wipe down all the vials to make sure there are no finger prints and I make sure there are no bubbles. I clean them with RODI after each use. I'm not sure what else I could do to improve the procedure.

I have a calcium checker, but I haven't tested it yet. I don't have a mag checker. Can those affect alkalinity? How all of these interact is still somewhat opaque to me....

You measure at the line with syringes. I made this mistake for about 3 months but it doesn't explain the change.

Large amounts of nitrate uptake by algae can convert nitrate to alk but the amount shouldn't be anything to write home about.

Is salinity constant? Could you have an issue with your ATO with siphons water out of the tank and replaces it with RODI? This has happened to me in the past and something you should observe.

 

[Randy Holmes-Farley Verified Community Expert]

There are many things that add alkalinity.

Two common ones are declining nitrate, and top off with tap water.

 

[monicalooze]

My nitrate has declined from 2ppm to 0ppm and alk has decreased one point. I top off with RODI. I'm so confused......

 

[Brandon3152134]

Are you sure your testing at the same salitiny everytime. That being a 10 gallon tank I'd say evaporated water may have a role in your weird test results.

 

[monicalooze]

Salinity has ranged from 34.7ppt-35ppt

 

[monicalooze]

I also have an ATO...

 

[Randy Holmes-Farley Verified Community Expert]

As I mentioned, there are many things that can slowly raise alkalinity, including slowly dissolving calcium carbonate sand.

That said, I'd keep watching it as the rise you report (9.4 to 10.3 dKH) is within the error specification of the Hanna alk checker.

 

[Scdell]

Get another Alk test kit. Hanna Alk reagents are all over the place lately. I bought a Salifert alk kit to test against Hanna. Hanna is higher than Salifert by more than 1.0 Hanna will read 9.4 Salifert right at 8.

 

[blasterman]

Salifert might have their issues, but their alk test is among the most reliable in my experience. Even at half resolution it's still better than most.