I just bought miracle gro organic choice potting mix. its the one in an orange bag. i want to use it as a substrate for my russian tortoise. i heard mixing it with play sand is a good idea. i hve been reading similar topics about this soil and some say they didnt find any problem with it, one said it had gnats but most of them said they have been using it for a long time and never had a problem with it for their reptiles/ tortoise. should i go for it? i still havent opened the bag. Thank you.