Can you share a full tank shot? Definitely something weird. Don't worry about algae or it looking pretty, everyone's tank sometimes looks off.
Walking through some things... First, your goby dying is hard to place any real meaning to. Mandarins require a very healthy copepod population or they starve to death. Your tank seems big enough in gallons, but it's also a tall tank versus a wide one, so you might have less rock and room for pods than you'd think, and that could just be starvation. Very hard to know without more history.
The cleaner shrimp surviving and inverts surviving is interesting. Shrimp are relatively weak and would die quickly if something like copper or chlorine was in the water. That does make it seem like maybe a disease issue.
The mollies living however imply it's not that. I've never heard of someone doing a chemical QT with mollies for saltwater. The pathogens in freshwater don't translate to saltwater and vice versa. The reason for adding them is if something is in the water they should immediately get it and die. I'm not really sure what would happen if you give them a prazi dose and then transfer them to salt, if it'd undermine that.
On the Molly being a bully, I doubt a molly is going to bully a saltwater fish to death, especially a clown. Unless it's not a molly.
On acclimation, if you're going from HTA to your house and have somewhat similar salinity, a fast acclimation is likely good. If that was the problem, the fish would die very fast. Keep it simple. Float bags. Wait. Open bags. Dump half the water in sink. Add a cup of water. Wait a couple minutes. Repeat. Don't check ph.
On the food mixing, did you leave it in the fridge or out, and how many days? I don't think a day or two sitting in the fridge is going to kill fish, but I don't know. I personally mix up a week of mix and put it in my fridge when leaving town. Though that was with freeze dried.
Do you have pictures of the fish when they died, or around the time before they died? Were they eating?
I'd start with the basics though. Before buying more animals:
1. Stabilize salinity. Get a reliable salinity monitor, at least a refractometer. Get the salt creep issue under control, it's probably a very small leak.
2. Stabilize temp. Hard to understand what you're seeing there, but buy a simple glass thermometer and use it as your reference. Do you have a heater in the tank? Make sure the temp is stable and accurate.
3. Stabilize nutrients going in. You should completely stop phytofeast. Start feeding only what gets eaten and doesn't make it to the bottom. With only a molly in there, it should be a very very very small amount of food. We're talking a couple flakes or pellets a day.
4. Buy a couple testers and post numbers (Phosphate, Nitrate most likely).
5. Do a water change, using water of similar salinity and temperature as your tank. Don't go crazy and do 80%, you'll kill the shrimp, but I'd probably do something larger (30-50% based on your numbers in 4).
6. While water changing, suck up any uneaten food from the bottom of the tank.
If the previous summary is right, you just have fish + inverts, you have effectively a Fish Only With Live Rock (FOWLR) tank right now. Those are relatively easy, and don't need supplements or special additives. Additionally N&P levels aren't that big a deal, but knowing is helpful anyway. So get it stable then
Walking through some things... First, your goby dying is hard to place any real meaning to. Mandarins require a very healthy copepod population or they starve to death. Your tank seems big enough in gallons, but it's also a tall tank versus a wide one, so you might have less rock and room for pods than you'd think, and that could just be starvation. Very hard to know without more history.
The cleaner shrimp surviving and inverts surviving is interesting. Shrimp are relatively weak and would die quickly if something like copper or chlorine was in the water. That does make it seem like maybe a disease issue.
The mollies living however imply it's not that. I've never heard of someone doing a chemical QT with mollies for saltwater. The pathogens in freshwater don't translate to saltwater and vice versa. The reason for adding them is if something is in the water they should immediately get it and die. I'm not really sure what would happen if you give them a prazi dose and then transfer them to salt, if it'd undermine that.
On the Molly being a bully, I doubt a molly is going to bully a saltwater fish to death, especially a clown. Unless it's not a molly.
On acclimation, if you're going from HTA to your house and have somewhat similar salinity, a fast acclimation is likely good. If that was the problem, the fish would die very fast. Keep it simple. Float bags. Wait. Open bags. Dump half the water in sink. Add a cup of water. Wait a couple minutes. Repeat. Don't check ph.
On the food mixing, did you leave it in the fridge or out, and how many days? I don't think a day or two sitting in the fridge is going to kill fish, but I don't know. I personally mix up a week of mix and put it in my fridge when leaving town. Though that was with freeze dried.
Do you have pictures of the fish when they died, or around the time before they died? Were they eating?
I'd start with the basics though. Before buying more animals:
1. Stabilize salinity. Get a reliable salinity monitor, at least a refractometer. Get the salt creep issue under control, it's probably a very small leak.
2. Stabilize temp. Hard to understand what you're seeing there, but buy a simple glass thermometer and use it as your reference. Do you have a heater in the tank? Make sure the temp is stable and accurate.
3. Stabilize nutrients going in. You should completely stop phytofeast. Start feeding only what gets eaten and doesn't make it to the bottom. With only a molly in there, it should be a very very very small amount of food. We're talking a couple flakes or pellets a day.
4. Buy a couple testers and post numbers (Phosphate, Nitrate most likely).
5. Do a water change, using water of similar salinity and temperature as your tank. Don't go crazy and do 80%, you'll kill the shrimp, but I'd probably do something larger (30-50% based on your numbers in 4).
6. While water changing, suck up any uneaten food from the bottom of the tank.
If the previous summary is right, you just have fish + inverts, you have effectively a Fish Only With Live Rock (FOWLR) tank right now. Those are relatively easy, and don't need supplements or special additives. Additionally N&P levels aren't that big a deal, but knowing is helpful anyway. So get it stable then
