Hi. 1) You should trust the calculators. They are invariably right. Why don't you trust them ? and 2) Can I sway you away from the stuff ? I have just sent back the 4 bags I bought because it is horrid. The Caribsea website says its up to 7mm in grain size when in fact I had TONS of bits that were up to 22mm in size.... practically rocks !!! It has no real benefit to the plants as it is not loaded with nutrients, and it is debatable as to whether the "bacteria" it claims to contain is actually any use. For the price, you could get something far better... Ebi substrate as sold by our sponsors Freshwater Shrimp is an excellent substitute, or even ADA aquasoil.