slow leak on CI baseboard (water heating) air pressure testing

I am installing #9 CI baseboard in one of my rooms. There are four sections in this big room. Three of them are longer than 10 feet. I did air pressure test on all of them with air vent installed. There is a slow leak on one of them. I can see the leakage is from the air vent with soapy water. The pressure dropped from 30 to 25psi in one hour. Doesn't matter how tight I turn the air vent, there is always a little. Is that small leakage will be ok when water is connected? The air vent comes with the CI baseboard. It is not the automatic air vent type. I changed the air vent. It seems both of them are not good enough. But they may be good enough for water?