I set up a 10gal Opae Ula tank about a month ago and added some brackish Malaysian Trumpet Snails and chaeto 2 weeks later. I started noticing some strange behavior with the snails, shell bleaching, and a deceased snail which I removed so I tried to do some troubleshooting online. I picked up an API saltwater master test kit as well as pH test with a better range.
Ammonia: 0.25
Nitrites: 0
Nitrates:0
pH: 6.5
I used RO water from my home unit and InstantOcean Reef Salt which I mixed to roughly half marine strength. I tested the specific gravity and it's about 1.011. The substrate is Caribsea Florida Aquarium crushed coral/aragonite which I rinsed thoroughly. There is are some lava rocks in there which I rinsed thoroughly and let soak overnight in some RO water. I haven't fed or added anything in besides a cheap aquarium light I got off of amazon which I have on for about 12 hours a day.
Someone suggested that high TDS could be preventing the aragonite from dissolving and buffering the substrate correctly so I picked up a TDS meter and checked. My RO output is a little high at around 30 ppm but the water inside the tank maxes out the meter at 9999ppm. I have no clue how this could've happened or what I should do. I'm shocked that the snails are still alive but they certainly aren't fairing too well. All advice is much appreciated
pH stuck at 6.5 and TDS at 9999+ppm
Moderator: Mustafa
Re: pH stuck at 6.5 and TDS at 9999+ppm
Hey guys, did some more research and it turns out I’m likely embarrassing myself here by over complicating things. My main concerns should probably just be the cycling and the low pH
Re: pH stuck at 6.5 and TDS at 9999+ppm
Of course your TDS is high, because you mixed salt into the water to make it brackish. 
That's why TDS measurements are useless for Supershrimp. How did you check the pH? With the carbonate in the salt mix and the calcium carbonate from your substrate it seems it's almost impossible for the pH to be at 6.5 in your tank. Your pH currently is most likely at around 8 where it should be. There must be some measuring error there.
As for the dead snail...it's hard to say what's going on without you sharing a picture of your tank and also details on what you put in your tank as decoration for example. So, post the picture/pictures and details and we'll go from there.
That's why TDS measurements are useless for Supershrimp. How did you check the pH? With the carbonate in the salt mix and the calcium carbonate from your substrate it seems it's almost impossible for the pH to be at 6.5 in your tank. Your pH currently is most likely at around 8 where it should be. There must be some measuring error there. As for the dead snail...it's hard to say what's going on without you sharing a picture of your tank and also details on what you put in your tank as decoration for example. So, post the picture/pictures and details and we'll go from there.