Re: Water changes start growth

     I experienced the same situation a while back--within an hour or so 
     after my 15% weekly water change, my plants would start to bubble.  
     This lasted for about 3 days, then there wouldn't be any bubbles until 
     the next water change.  I fertilized regularly with Flora-Boost.  I 
     eventually attributed it to CO2.  My tank would have a CO2 
     concentration of 0-1 ppm before the water change, but afterwards the 
     CO2 would be about 4-5 (according to LaMotte).  This prompted me to 
     add CO2 via yeast-sugar, then I graduated to a 20# cylinder.  Now, my 
     plants bubble all week (with the lights on, of course).  They no 
     longer "respond" to water changes like they used to.
     However, you stated that you already add CO2.  Perhaps it isn't 
     completely dissolved or is being diffused out too rapidly.  I am not 
     convinced that it is any other macro- or micro-nutrient that is 
     causing this, as photosynthesis requires light, CO2, and water to 
     occur (Growth requires N, P, K and micronutrients).