First of welcome to the forum!
Before I comment on the water altering stuff...I read here that you wanna have Shrimp, Kuhlii and Goby and Neon all in the 30g - Right?
The Shrimp Kuhlii and Neon I can all see in one tank; The Bumblebee not so much cause they need salt added, their needs are in ranges of pH 7.5-8.5 hardness 10-20 Salt strength around 1.005sg.
That said the salt will NOT work for the shrimp for sure and not good for the Kuhlii & Neon neither however your water at least judging from your pH reading will work for the Goby's however then you need to find them other brackish tank mates.
9 times outta 10 its a LOT safer and makes for a good long term health of the fish to not mess with your water, yes you'd be on the higher end for the Goby but I'd find that MUCH safer/ healthier from my exp then messing with it, especially these chem's offered at stores - Don't use them that'll produce permanent up & down swings for the fish and that's really not good at all to say the least.
Now if I was you in this situation I'd set up the 10g for the shrimp; the 1 single Neon I'd honestly either give to someone who has Neon's already or simply back to the store. So you could set up a nice home for the remaining 2 Guppies and the shrimp.
For the shrimp part and the shrimp you want I'd suggest checking these 2 sticky notes http://www.tropicalfishkeeping.com/f...y-chart-37011/ http://www.tropicalfishkeeping.com/f...keeping-37012/
This all said if you decide to go a different way since the Goby need salt and indeed want to soften up your water the safest and best way really is to use peat, plain peat no ferts or nothing added, just plain organic peat add to a lil sock/bag whatever you have and hang it into your tank close to the filters outlet. Now this method will not magically over night soften up your water, it will gradually soften it which is a save method if you already have fish in there and it keeps it stable. However as good as it works there's 2 "down" sides 1) it stains your water a lil like tea which is actually good for most fish cause its natural to them but some people are bothered by the look (I love it thou) 2) Peat only works for so long essentially the harder your water is the more often you'd have to exchange the peat for new; in my case I had pH 7.8 or 7.9 and lowered it to 6.5 for Killi and I exchanged mine about 2x year. If you look at my aquarium log here you can see my "Killi" tank as well as the "African Dwarf frog" in both set ups peat was used. http://www.tropicalfishkeeping.com/p...hp?userid=1029
Last but not least to toss in another option to all this: Get fish that suit your water.... There's a variety of colorful smaller cichlid fish that would do wonderful in your water, pers Livebearers I would not get simply cause they have too many baby's and overcrowd your tank in no time.
Now I think I covered it all for the moment