I suddenly need a 50% higher alk than Ca dose, any ideas?

[Fritz05]

I have a 65g mixed reef and use Randy’s 2-part dosing:

380 g of soda ash in 1 gallon of water
450g of CaCl in 1 gallon of water
90g of Balling Part C with 100 g of Seachem Reef Advantage Magnesium

For a long time my daily doses were

100 ml of the soda ash solution
95 ml of the CaCl solution
200 ml of the Part C plus Mg solution

Alk was stable at around 8 and Ca at 450ppm.

Over the last two months I had to increase the soda ash dose to 130ml per day to maintain stable alk.
My Ca-levels increased to 520 without an increase in the dosing of CaCl.

I have not changed any livestock (only last week I removed two larger SPS colonies).

I use the same bag of soda ash. It has not clumped and its pH is strongly alkaline, so it has not turned to sodium bicarbonate.

I tested Mg, and while I know Mg tests are not very accurate, it showed 1400ppm, so appears fine.

Any thoughts would be appreciated.

 

[rishma]

A helpful article

https://www.reef2reef.com/ams/when-do-calcium-and-alkalinity-demand-not-exactly-balance.954/