People experience lots of problems all the time, but discovering the correct reason for those experiences is actually very difficult.Point is, it's my experience that it has happened! No expert needed there
It wasn't very long ago that people blamed Nitrates and Phosphates for their experiencing algae problems in their tank. This debacle went on for years until someone demonstrated that the reasons were exactly the opposite and that adding Nitrates and Phosphates to the tank actually improved it's health.
It turns out that in CO2 injected tanks, by far, the most problems incurred is algae due to poor implementation of CO2. So adding CO2 to a tank is certainly no guarantee of success or of improvement.
CO2 should not be viewed as a pill that you give to the tank. It's a serious undertaking and when you enter the CO2 arena, how you manage the tank has to change. Adding CO2 means being vigilant about nutrition and keeping the tank clean. CO2 increases the amount of nutritional uptake by the plants by up to tenfold and this consumption results in an exponentially higher level of organic waste in the tank.
The delivery of CO2 must be even AND must be stable. As I mentioned, the sudden increase in CO2 availability triggers to plant to reduce it's production of RuBisCO, the CO2 gathering protein. Once the production rate of the protein is reduced, it takes weeks to then increase the production rate if the CO2 levels fall. So if your CO2 is implemented poorly this results in a rate decrease, then a command to increase, and so on. During the time that the RuBisCO level has fallen, if the CO2 levels also fall then the plant will actually suffer a CO2 shortfall because it is unable to collect enough CO2 due to low RuBisCO levels.
This is why we see CO2 related problems and CO2 related algae in CO2 injected tanks.
When you add CO2 therefore, you must implement it wisely and with purpose, not just because you are bored.
The CO2 levels must be at it's highest value when the light turns on.
It must remain at or near it's peak concentration level for 3-4 hours.
After the first 3-4 hours, it doesn't matter if the levels start to fall because the plant will have eaten it's fill.
The distribution of CO2 must be even across the tank in order to allow the RuBisCO production rate to remain stable and to be in concert with the actual CO2 concentration.
Attention must be paid to the nutritional uptake otherwise, nutritional deficiency related algae will attack.
So your explanation of WHY you got algae when adding CO2 has nothing to do with why you actually got algae.
Undoubtedly, there was a failure in one or more of these areas, which triggered a algae bloom(s).
Cheers,