No way 2 300 watt heaters will be able to maintain your steady 90 degree temperature, even with a properly built insuated lid, it would be nearly impossible since you have such a huge volume of water. And you want to filter your 8x4 with a fluval 303? I wouldnt even trust 4 fx5s to do that job, let alone 1 small canister. Just equipment alone will cost you way more than the $1000 needed to buy the 6x4 tank lol. I guess you could cut out the filtration if you were planning on doing plants like the guy in the article you quoted from. Eventually, your electricity bill also will just leech you dry especially since your pond is in your basement.
