I am probably going to be disowned for this

I think many people do an opposite lighting schedule to their DT for pH purposes. The chaeto was doing fine with the 12 hr before. Is there any other type of algae that releases chemicals to inhibit nearby macroalgae growth? I feel like I may have heard that somewhere?

 

Um so I tested my nitrates yesterday and they were 0. I retested. I think it is the 24 hour light cycle and chaeto. I am in disbelief - I may bring a sample to LFS. This solution was just too easy.

How long will it take for algae in DT to die off? My sump is filled with algae and this 24 hour light cycle is causing it to grow out of control.

 

So, it sounds like testing error really. Maybe a combination, but nitrate test its have a lot of issues. While changing the lighting schedule, probably can help some IMO, as algae like most organisms has a built in clock that is entrained to light cycles. It's pretty safe to say that it didn't drop your nitrate 20ppm overnight.

Is this a 90g system?
If so, that means your cheato would have needed to grow quite substantially. You would have added about 27g of dry weight. That is a lot for cheato, as it really dosn't weigh much dry...