Hi Denis,
You're very welcome!

I'm sure we can whip that tank into shape! I guess I'm not really sure exactly how you are preparing your mixture but KH2PO4 is a fairly soluble powder so if you are having trouble dissolving it you should just add more water to your solution. If for example you prepare a 500ml solution and you intend to dose say, 50ml per dose, then just add another 500ml to it (giving 1 Liter) and then dose 100ml instead. You should never have to grind any of these powders up with a mortar&pestle.

In any case if you were to shake up the bottle and dose the particles will immediately dissolve in the tank within 5 seconds. You need to use a large quantity for your solutions, or make up a shorter term solutions with less powders. If you check the Dry Dosing article=>http://www.ukaps.org/forum/viewtopic.php?f=34&t=1211 you'll see where I gave the standard example for a 4 week dosing supply for a 20 USG tank. You would scale everything linearly for your size tank but at 74L you can use the numbers directly. Here is an excerpt from the article which you can use without any modification:
NPK (Nitrogen+Phosphorus+Potassium) Mixture for 20 Gallon Tank
1 month = 4 Weeks
3 doses of NPK per week
Therefore there are 12 doses of NPK per month.
Multiply a single dose teaspoon value by 12 => [3/16 tsp KNO3]*12 = 2 ¼ tsp KNO3
[1/16 tsp KH2PO4]*12 = ¾ tsp KH2PO4
[1/2 tsp MgSO4]*12 = 6 tsp MgSO4
Add these to 600ml of tap or distilled water
Now this mixture must serve 12 doses so each dose is 600ml/12 = 50ml
This makes life easier because you need only dose 50ml of this NPK solution 3 times per week.
Always separate the CSM+B from the NPK because it has a tendency to react with the phosphate. You can dose the CSM+B as a powder or if it more convenient add 8 * 1/16 tsp => ½ teaspoon to 300 ml of water and dose 25 ml two times per week.
Naturally, the mixture scales in the same way. If the tank is twice as large than you would add twice as much powder to you 600ml of water and so on.
Green water seldom goes away by itself. If you don't want to buy a UV then you'll have to do massive multiple water changes per week combined with better dosing and stable CO2. That's the brute force method but it will take some time I'm afraid. UV
is the best method actually.
I hate to rain on your parade but that thing about lowering the light fixture? Major, major bad idea right now with rampant algae problems I reckon. If anything you should move it up by about a meter
away from the tank because light is algae's second best friend, remember? Well...a meter is an exaggeration but you get the picture, right?
Have a think on the above and let us know if there is anything unclear.
Cheers,