Hi, I have 4 Geophagus in my 200gal tank. I have 1 Altifrons, 1 Orange Head Tapajos, 1 Sveni and 1 Red Hump Eartheater (I am aware that i need to get some more, I will be doing so next week.) In the tank currently is gravel (smooth, squishy like gravel, 2-3mm, with small rocks that the Geophagus have been spitting out) that came with the tank, and I used it at the time. As the tank is so large, getting all the substrate out while maintaining these fish will be quite difficult. So my question is, can I mix pool filter sand with this Gravel and provide a good environment for my geos? The geos have been on gravel for awhile and seem to be doing okay. But it does not sit well with me because I know they are sand sifters. Will this work?