I am thinking the pH range in your bog would be best somewhere around 6.5-7.0 in my opinion however this varies considerably based on region and species planted so best to get more input from others. The pH range in a herp/fish pond should be more toward neutral. Nothing kills off herps and fish faster than rapid pH changes. pH fluctuates throughout the day and also based on other factors so if possible try hard to test at the same time of day when you do your tests. I find my wildest fluctuations occur in the fall because of oak leaves dropping in ponds and after a heavy rain. Sometimes I adjust the pH a tad, sometimes I leave it be. Depends on what the averages were the week before.
I saw photos you posted of your property. Beautiful, absolutely beautiful and when can we all move in with you? Just teasing. If you dig/connect a herp pond to/in the area you are going to use as a bog, you will most assuredly have a logistical nightmare stabilizing the pH in the pond. I am pretty sure the water will never be clear which bothers many people. No matter what type of hi-tech bio filters or skimmers you connect to a pond in that area, you will be very frustrated and I'm thinking you will rip all of your hair out within one season and be willing to accept that 4th corner over there at a funny farm with me, April, and Rattler. Please check into positioning a pond at a higher elevation closer to your house and as a separate entity from that low area. Other than pH headaches, the big concern is that knock down gorgeous picture perfect lake back behind your home. I'll step right out on a limb and suggest that you really need to seriously consider going a 100% native. I am relatively sure a probability for "seeding" your lake exists as well as any waters that flow downstream from your lake with any plant and animal material you might place in a pond or a bog regardless of where they are situated in your backyard. It's the proximity of that lake to the area in which you will be working that is sending up red flags. The potential for seasonal flooding may be very real. In a situation such as that which was described above and that which I saw in your photographs in the other thread, one might want to weigh the benefits of using native plants exclusively whether it be a CP, bog, woodland, prairie, or marginal species. I know you never mentioned adding fish but most people can’t pass up the pretty goldies and within a year or so, they’ve generally added fish from PetSmart or WalMart- I know I did. They always seem like such a natural to add to a herp pond. Exotic carp and/or exotic turtles, as well as any other non indigenous fish or herps, really should not be used either as whatever would be stocked in a new pond would be quite capable of ending up in that lake. Point in context is what happened here by me the spring of '04. That was the second hundred year flood in 10 years and the third 100 year flood in 15 years. Contents of people's bogs and ponds were washing into the Des Plaines River as well as into naturally occurring wetlands. The Des Plaines River was spreading all that non indigenous flora and fauna into other bodies of water as it swelled and spread. The Des Plaines River is a natural waterway not so unlike the creek on my property that flows down and into the Des Plaines River. They are connected so they are one. In a perfect world; accidental discharges of pet goldfish/koi, red eared sliders, and non indigenous plant materials don't end up in natural waterways. Sadly, we don't live in a perfect world and rains from the heavens often thwart our best efforts to eliminate any and all possibilities of introducing exotic species to natural bodies of water. Needless to say numerous species of both plants and animals were unintentionally introduced to an already taxed watershed because many people didn’t know any better.
Building a pond from scratch in a different location and at a higher elevation with an EPDM liner and the right equipment will be considerably easier to maintain, more herp friendly, and will have less potential of negatively impacting the environment than taking what appears to be the path of least resistance. I'm writing from actual experience here and no need for you to get hit by a Mack truck like I did and have the Army Corps of Engineers crawling all over you while holding an aerial view of your property evidencing disturbances within 100' of water. I have two natural ponds on my property and numerous others that I created either for herps or for my Wakins. Wakins are a non indigenous fish but that particular pond is at an elevation of 786’ above sea level. If water gets to that area, my entire community will be nothing but chimneys poking up through waves as that would be a flood of Biblical proportions. That is my only pond that has non natives in it and it is right by my front door and the fish were gifts- ugh.
Here's a great book you might want to consider picking up at your local library- Lakescaping For Wildlife and Water Quality by Carrol L Henderson, Carolyn J Dindorf and Fred J Rozumalski. If you are interested and can’t get your hands on a copy, I will send you my copy and you can just return it when you are finished. I recently recommended this book to somebody else and it addresses many issues that will confront you.
You and I are within 100 miles of each other. It would be my pleasure to help you with both non CP plants and critters for your very worthwhile project. Plants I would be more than happy to mail to you- my treat. Critters you would have to come and pick up or meet me somewhere in Milwaukee to get as I can't bear to ship a live fish or critter. And, 95% of what I have added here is native non CP species so that's what I have to share. Please take me up on this offer if you go the route of a pond as there is nobody out there with whom I can share anything as I pretty much have but only one CP of each listed on my grow list so those are out to share for a few years.