Actually.. the natural salinity level of the ocean is 1.026.. and fish and inverts both share the ocean. I've never heard of inverts liking lower salinity levels than fish. Crepe, you must be thinking of Nitrates. Inverts, including coral, don't respond well to aquariums with high levels of Nitrates. However, fish on the other hand, can survive in very high levels of Nitrates. I think there was a thread opened by Floyd R Turbo about one of the tanks he maintains, and one tank had something like over 300ppm of nitrates.. i think that was the number. Yet the fish were still living. But there were no coral or inverts in that tank.
As for the test kits, it's a little shocking that you even started a tank, regardless of whether it was FW
, without test kits. And since you don't have test kits, i can only imagine that your tank isn't cycled. Which means.. unless you do tons of water changes, your livestock is more or less going to die. All of them. Including the coral you bought.
Oh yeah, and the green hair algae doesn't mean that there is ammonia in the water. GHA is caused by many things. Overfeeding, nitrates, phosphates, keeping the lights on for long long periods of time.. and there are so many more things that contribute to hair algae.
Honestly, in this situation, i would first go out and get a test kit. Even a test kit for the simple things like nitrite, ammonia, nitrates, etc.. is better than not having a test kit at all. You need to test your water, and see what the results are and then post them here so we can give you advice and what it is you need to do to keep your livestock alive. And if it's really bad, you might have better luck just returning your livestock so they don't die, and then starting the tank over. Properly this time.
But the first step is to get a test kit and post your water parameters here so we can help you.
Hope this helps.