I suspect 6.8 will be quite similar to 7, but will just take longer to cycle. I did see an explanation of the NH3/NH4 ratio on here (possibly @essjay ???) but I confess it was way over my head.What about our tanks that are say 6.8 ph. Then what?
What we do see a lot on here is people with a pH in the range of 6 - 6.5 who don't undertstand the cycle and add fish (as advised by LFS) and then keep adding fish at 2 weekly intervals. Then one morning they wake up to a tank full of dead fish. My explanation for this (may not be correct) is that it takes much longer for the nitrosomonas to establish and there is no loss of fish because NH4 is much less of an issue than NH3. Then eventually the nitrosomonas does establish and starts turning the NH4 into nitrite. So you end up with lots of nitrite very quickly (lots of NH4 to feed on). At this point there is no nitrobacter to turn nitrite into nitrate and fish start dying