Just got some K2SO4 and some KH2PO4 -- what's the best way to introduce them?

Ok, I just noticed this thread after responding to the other one. I'm gonna assume that the Potassium Sulfate is a fine white powder. I add 1/4 tsp. per 20-30 gallons, directly into my HOB filter. If you'd feel better, dissolve it in a little water and pour it into either your filter or a little at a time into the tank. The PO4, again, I'm assuming you got Fleet Enema which is a liquid. Add 2 drops per 20-30 gallons directly into the tank. If it's not a liquid form of PO4, Tom Barr prescribes 2-3 rice grains worth. You have a relatively low light set up, so start light with the dosing and see how everything reacts(pearling/growth. Dose the Potassium after your water changes. And dose the PO4 after the water change and again in the middle of the week.
I STRONGLY SUGGEST that you wait a while to up your lighting as the more light, the more potential for disaster. Trust me, I've been there. You can always go with more light once you realize the value of learning the balance of your tank.
Len

Do you have a PO4 test kit? pH,nitrates, an PO4 are important IMO. With those you can monitor the important additives that, if over-dosed can be harmful. pH will tell you your CO2 level and the other two will enable you to keep your other parameters right.
With the plant load you're carrying you could approximate your dosage of PO4 and not over dose. You know how big a rice grain is. Now take two rice gains worth of the powder and either add through the filter, or mix with a small amount of water and add it to the tank. I estimate that a drop of Fleet Enema to be one rice grain's worth and add 2 or 3 to my 55 gal. tank, and when I test I get a 1.0 reading, which is entirely safe. And you wouldn't believe how fast that reading drops in a couple of days.
The plants just eat it up. I dose that amount of PO4 at least twice a week to keep it where it's supposed to be. I do the same for the nitrates, but don't have to add KNO3 nearly as often as PO4. I could never just make up a batch of PMDD and dump them in. The dosages are based on need which I base on testing. Hopefully it'll level off and I can get to the point where I'll know how much and how often to dose what without having to test as often. The potassium, to me isn't as critical because it's not toxic.
But I follow Tom's advise and only dose that after my water change. And the water change resets the tank should I over dose something during the week. Incidentally my water changes are between 30 and 50%. They don't, IMO have to be exactly 50%.
Len

One more Thing

For a better understanding of nutrients and fertilization, go to the search engine(upper right part of the page) and click on it. Type in either Tom Barr or Plantbrain. His advise is always consistent on these topics. You'll learn a lot.
Len