I just like to keep the water line lower for the arowanas, don't want them to jump and hit their heads on the lids, or even worse, decide to investigate the lids, and do some carpet surfing....
I have run this way for years, and never had a Asian Aro jump out...I have never placed any weights or locks on the lids.....fingers crossed!
i think you stand more risk of the aro jumping out with low water level as all the aros power comes from the last flick of its tail when it leaves the water
with a high water level the aro doesnt get the chance to use the last flick before it hits the cover glass
aros dont take a run up to their jump its all one smooth movement