I think a great number of people have given information and suggested to stop what you're doing in terms of adding new things and read. Some great sources were given. This forum is a great resource, but the initial groundwork needs to be done. Some of the basics that would be covered in any book are quite frequent questions of yours and some of the same topics (I do believe) have been covered in other threads. So, please understand that there may also be frustration (at least from me) when we've got some live animals involved.
never add anything to your tank without measuring. Then, your reasoning behind adding what you did to increase the entire SG up is mistaken. if I add in one gallon of water with an SG of `1.024 to 74 other gallons of water which are at an SG of 1.020, it's not going to change the SG much at all. This isn't simple math we're talking here to raise the SG. It's a slow and methodical process to not shock the system. My mind tells me that the SG of the water you added didn't really change it much.
Invest in your own testing equipment. the tests that the store is running for you in terms of ammonia, nitrate and nitrite are going to cost a measly $20 or so for some basics (cheap is better than nothing, IMO) plus hydrometer.