Hi,
Your situaiton sounds similar to mine. I'm using an Eheim 2260 with the 1262 pump (3,400 lph) on a 1.5m tank. My spray bar is 1.3m long. I'd recommend reading my thread for more detailed information:
http://ukaps.org/forum/viewtopic.php?f= ... 10#p242117
By the way, I wouldn't go with a pipe with 15mm ID as this is roughly 7 or 8% less than 16% so you'd instantly lose a few hundred litres per hour. As was explained to me, you need to keep the diameter at 16mm or larger to maintain the maximum amount of water processed each hour.
As you can see in my thread I am stretching the 16/22mm tube over 1/2inch PVC. This has an ID of 18mm. So the outlet starts at 16mm and then goes into 18mm. The trick now however is making the total area of the spray bar holes equal 16mm. If the total area didn't equal 16mm then this is when I saw uneven spray / flow through the bar.
Clive gave me a formula for working out the hole size based on quantity / spacing, this is in my thread.
I've been playing around with various spray bar designs over the last couple of weeks. Initally I started with 33 holes (see videos in my thread). Since then i've tried around 4 or 5 different versions.
For me the best appears to be 26 holes at 3.2mm every 2 inches. Water is hitting the glass evenly and with plenty of force and there is movement all throughout the tank.
Also, I've noticed that the angle you drill the hole has a slight impact so try to drill the left side holes on a slight angle (coming in from the left), the middle ones square and the right on a slight angle (coming in from the right). It's hard though and you'll probably only see what I mean after you've made your first one.
Please update with your findings and some pictures.