Example, taking the valve off the Pyrolox filter is not going to pull the DT up (but you mistakenly think it will). The bottom basket is very unlikely to be blocked up (but you think it probably is). But the Pyrolox is, and the only way to see if it is, you dump it out of the tank. Which makes it very easy to then remove the DT and look at it. When you dump it the gravel underbed will come out mixed with the mineral and you won't be able to separate the two so you'll have to solve that problem before putting the filter back together. Usually it's best to buy new of both replacing the old.
And when yer all done, the amount of chlorine you are using is not going to kill IRB or oxidize much if any iron or H2S gas to speak of and within months the new Pyrolox will be like the old is now and you'll be looking for a new solution while being substantially poorer and more frustrated. And I may still be here to tell ya "see, I told ya so".