As stated in the topic, these scratches/cracks have been on my acrylic for over 10 years and I have had this tank for about 15 years now. My tank is a 60g rectangle (48 x 15 x 18) "Clear for life". With that being said my acrylic should be 3/8 inch thick, but have no idea how deep the scratches are and they are 0.75 - 1.5 cm wide. How worried should I be and I have never used the weld products.