I'm going crazy with this...
I have a Taq from Biotools that comes with buffer with MgCl2, buffer without MgCl2 and MgCl2 solution.
I used to perform colony PCRs almost everyday and it always worked with the provided buffer with MgCl2. Always getting clean bands.
Untill one day when buffer with MgCl2 finished. I replaced this buffer with the buffer without MgCl2 and added MgCl2 separately so the reactions could have the same concentration of MgCl2 as the one provided already with MgCl2 (2mM).
The only thing that changed was the buffer and it just stopped working.
When I run the agarose gels, in the reactions from colonyPCR I get a huge amount of dna that does not go far from the well and the controls show a strong band with a shorter size than expected (~750bp). It seems that the expected band is there (~1.000-1.200bp) but it's too weak... Some smearing can also be seen... Negative controls (without dna) are 100% clean.