I have a 240 and a 125 and every 4 or 5 weeks the store comes over to do a water change and it's 200 for both tanks. That's alot I think. But if I buy the water from them it's not much less. I have about 5000 dollars in animals in there. Is it better to just leave this to them? Or should I chance mixing it myself and possibly screwing it up. Thanks guys