I will be using ppg paint and hardener. I have a different brand of reducer and I'm wondering if it's ok to use that?

Better to stay "within the system" as that's how paint products are developed & tested. That said, I know that you can use certain DuPont reducers with Standox paint products, and plenty of people do mix brands. You might try painting something and see if you get good results.

No I wouldn't. I have used different brand products on top of one another, but never have mixed brands when mixing paint.

I bet some one will come on here and say they have done it and it won't surprise me, but I won't ever take that chance because paint and prep work cost way too much today.

Are you a gambler? As already stated, paint is already too expensive to take it back off and start over. How much TIME do you think that will cost you? Buying the correct reducer is the only choice.

Gary I will be that guy! What brand of reducer are you going to use? Reason I ask is this. Transtar reducers are suppose to be equal to DT reducers. I have sprayed a lot of Transtars basecoat and they say to use either thier reducers or DT or a urethane reducer BUT NOT shop line reducer. I have been in a pinch and used DT reducer in shoplines primers before. Now would I use Transtars reducers or shopline reducers in say Ppg colors or clears. Nope. Would I used DT REDUCERS in Transtar clears if it called for it(which they don't btw) nope. Only time is in thier base coats and that's coming from their tech guys as well as district rep. Not had any issues with that. Now I can clearly see PPG rep telling you noway can you do that and would tell you DT and shopline reducers are different animals and not to intermix them. Best advice is to keep in the system.

if you really have to use a different reducer because your stuck, the general rule of thumb is keep basecoat reducers with basecoat and keep 2K or top coat reducers with topcoats,basecoat reducers generally dry quicker so you don't get solvent retension in your clearcoat, and topcoat reducers stay wetter so your paint has time to flow. Using a topcoat reducer in basecoat can cause what we call solvent boil( the final finish looks like it has small pimples)