“Hard water” stains above water line

[Eddie K]

Hi everyone. Im cleaning my old aquarium to sell and there are these hard water stains above the water line left over after cleaning with razor blade. This is what I have tried:
1) vinegar soaked paper towels x 45 min - no change
2) Mr Clean sponge - no change
3) Soap/water - no change

I really dont want to try CLR. I have not tried citric acid because I feel like it wont help

See pic.

 

[Jay Z]

If it’s calcium based some muratic acid thinned out should work. Easy to test. When it hits it, if it turns white really quick, it’s working.

Where elbow high gloves. Just use a rag or dish sponge. Do it out side. Have some baking soda on hand just in case. First to neutralize if you get any on your self. Second to neutralize the tank after you clean it.

 

[328 reef]

I use apple cider Vinegar.

 

[Eddie K]

Tried muriatic aid ... diluted 6 cups in 2 gallons of water. More then the recommended 2 pints in 1 gallon on the bottle. It maybe worked on the sides but the front still looks the same :-(