cloudy tank

Question
Hi, I have an 2 year established freshwater 20 gal tank with 6 cory cats and 1 10" pleco. All was good but the temp was a little cold, 65F. Fish were thriving but I was concerned. So, after a full gravel clean and full water replacement things were fine for a week but I finally  decided to address the temperature issue and added a decent heater that went over intake and temp came up to 74F and fish seemed fine but after 24 hours the water got cloudy. Never had this issue and always cleaned (vacummed & changed 25% water every 4 weeks) with good results. Any thoughts?
Thanks
Bill

Answer
Hi Bill;

I'm so sorry to have taken so long to answer your question. My computer was down and we had an emergency with our water system here. All is fixed and all okay now so here I am. Finally...

I think the problem with your tank is simply that with cleaning it so well it has thrown the system into a break-in period, almost as if the tank was started new. The beneficial bacteria that keeps your tank clean and clear has been disturbed or killed off to the point that it can't do it's job as effectively as it used to yet. Hopefully there is still enough of it left to get going again very soon. You might want to monitor the ammonia and nitrite levels to make sure they don't become unsafe. Those are the fish waste toxins that the beneficial bacteria control. If they are elevated to an unsafe level you will want to make partial water changes of no more than 25% to lower them so the fish can tolerate them until the system finally balances out again. Your test kit literature will tell you what the levels are and where they become intolerable. I hope everything turns out okay. Let me know if you need more help...

At Your Service;
Chris Robbins