0.8 dkh in 2 days???!!!!

[VR28man]

Hey all,

Experiencing some wild flux in my measurements.

Two days ago (Monday morn), my alkalinity (after dosing 1/4 tsp baking soda; prior it was 154-7) was between 166-170ppm (I use the Hanna ppm checker). After 12 hours, it was 177-8 (Monday night). Today (Wednesday) morning, it was 160-2.

I find this flux very odd, and am wondering if anyone has experienced this before and could offer ideas on what the problem is.



Background:
- objective is to hold alk at around 165.

- Hanna checker is done twice "correctly", and then 3-5 times using a reagent-less test vial and one with reagent (contrary to directions; I've found this to be essentially consistent with the "correct" method)

- tank is 29 gallon, fairly low fish/coral load, but recovering from a massive cyano problem and nutrient surplus. Nitrate has swung from ~25ppm two months ago to ~1-2ppm one month ago (after allow Seachem Matrix, Purigen, and Phosbond to settle in a closed off area) to ~10ppm now (perigen removed and the remainder cleared of lots of accumulated detritus), measured via salifert. Now there is only a minor hair algae or cyano problem, in contrast to previous months. Purple and green coraline growth is decent. CA ranges between 420 (one month ago) and 450 (Sunday)

 

[Tautog]

Your using baking soda? Straight? Un-baked?
If so, for a tank so small is very dangerous. Your Alkalinity is properly very high, straight baking soda will do that. Bake it, and it turns to Soda Ash, which isn’t as powerful as baking soda straight.
I’m adding the same stuff you have, but high nitrates aren’t all bad. I’ve had high nitrates, but a little algae is good. If your not using a R/O, start. I have never had any hair algae.

 

[VR28man]

Your using baking soda? Straight? Un-baked?
If so, for a tank so small is very dangerous. Your Alkalinity is properly very high, straight baking soda will do that. Bake it, and it turns to Soda Ash, which isn’t as powerful as baking soda straight.

Very small quantities. As in, generally 1/8 teaspoon (.75mL), mixed into a 100ml beaker of tank water. 1/4 teaspoon (1.5mL) seemed to be too much, with an apparent 10-20ppm shift.

I have been looking to add a small amount daily (e.g. 0.3mL), and was going to start that in a day or two once I measure alk going below 160 ppm.

 

[Tautog]

Using even small quantities of baking soda can cause large swings. I wouldn’t do it, your asking for trouble

 

[Randy Holmes-Farley Verified Community Expert]

I don't think these are big swings, and the checker itself has a claimed uncertainty of +/- 5 ppm in each measurement.

Most people consume 0.5 to 3 dKH ( 10-50 ppm calcium carbonate equivalents) per day.

 

[dimo]

Very small quantities. As in, generally 1/8 teaspoon (.75mL), mixed into a 100ml beaker of tank water. 1/4 teaspoon (1.5mL) seemed to be too much, with an apparent 10-20ppm shift.

I have been looking to add a small amount daily (e.g. 0.3mL), and was going to start that in a day or two once I measure alk going below 160 ppm.

Don't use tank water when you want to add baking soda. There's calcium in the tank water that will cause precipitation when you add dry powder to mix. Use RODI water.