Dropping and then rising alkalinity

[Domizi]

Hi all!
My tank is 1 year old, and I have a weird occurence. When I started out with only fish initially I tested alk just to see where it was at. Found it at around 5, although my water should have mixed at least 6,5. Tested the mixed salt, and saw that it was mixing low (6,2-ish). I usually dosed a little alk each week here. At the same time I got a bad case of cyano which took a long time to get rid of, even with nitrate at 5-10 and phos at 0,05.

Now the tank looks great, have switched salt to one that mixes at about 7,2-7,6, but my alk is rising. Is it something that was stored in the bacteria that is now released, or in the marco rocks?

 

[Randy Holmes-Farley]

Bacteria cannot consume or store alk, except as they produce or consume nitrate. Rising nitrate depletes alk and falling nitrate adds alk.

Other processes, notably precipitation or dissolution of calcium carbonate can alter alk. If demand is very low, slow dissolution of rock and sand can slowly raise alk.

Other additives can also impact alk without telling you. Amino acid dosing, for example, depending on how they are formulated.

 

[Domizi]

Bacteria cannot consume or store alk, except as they produce or consume nitrate. Rising nitrate depletes alk and falling nitrate adds alk.

Other processes, notably precipitation or dissolution of calcium carbonate can alter alk. If demand is very low, slow dissolution of rock and sand can slowly raise alk.

Other additives can also impact alk without telling you. Amino acid dosing, for example, depending on how they are formulated.

Thank you so much for the reply, I've really been wondering since my alk is up to 9,6 now. I have a low demand so far (small montipora, cyphastrea and hammer all added recently). I am not adding anything other than modern reef nitrate and phosphate additives in small amounts each week as the consumption is larger than the natural addition from foods.

In other words, this should sort itself out with time?

 

[Randy Holmes-Farley]

If the cause is some slow addition of alk and you boost the alk demand, yes. :)