At a pH of 7.5 and a KH of 3, your CO2 level is at 3ppm.
You need to inject more CO2 or check if your CO2 injection system is efficient.
At a KH of 3, you need to inject enough CO2 to bring the pH down to 6.6. This will give you a CO2 level of around 25ppm.
What is your light level? and the size of your tank? CO2 without at least 2w per gallon won't do very much for your plants; best is the two together.
"...still alive and actually growing..."
is not what you want.
What you want is "my plants are growing like mad and look fantastic! I need to prune them every week!"
If your light level is at least 2wpg and you get your CO2 up to 25ppm you'll be amazed. I think we all were the first time went down this route.