A little backstory: I bought a used 40 gallon set up (tank, stand, lights, everything you need) for 50 bucks and got the tank home only find a crack when cleaning it. I ended up special ordering a new tank (38gal) that will fit the set up. I have two 20 gallons I'm planning on eventually merging into the new tank. In order to save on costs (did not anticipate buying a new tank for this adventure), I was thinking of mixing the substrate the cracked tank came with (green regular substrate, nothing special) with the CaribSea Eco Complete I have in one of my 20 gallons. I'm not really a fan of colored substrate and prefer a natural look, but I'm thinking that mixing it with the black CaribSea will look all right. The tank will be planted. Is mixing a good/bad idea? I've read mixed opinions.