these are statics right?
have you tried the static apnea tables? I recommend Table B, start around 30 seconds and work your way up to a minute or more, you can customize the times to suit your needs.
LINK>
Static Apnea Tables by Freediver.co.uk and Freedivers.net :: Graphics by Mozzi
the voice prompt is really nice too.
the idea is to increase your time by 15 seconds each hold to just beyond your normal hold time by the 8th hold. wait 30-60 mins and repeat once or twice. Later you can work in dynamic exercise prior to the static practice to condition yourself under an increased heart rate. but that is something different than just surpassing a static PB of 2:30.
it is hard at first, but if you use your break time wiseley during the static apnea table program, e.g. focus on slow deep breathing, and concentrate on staying calm, and watching your time limit till hold you may easily surpass your current PB with a little practice.
I wouldnt push your self to black out too much either, try to avoid samba (fuzzy stars in your vision, and light headedness), and avoid blackout.
if you avoid blackout, you will be training your body to cope with higher levels of CO2 a little at a time, and your mind will relearn new limits.
if you push to black out is is sort of like resetting your Oxygen urgency clock to 0, at least that is what it feels like.
as for food, a medium snack, or a light meal, not to full, but personally, I go spearfishing on almost empty, maby one P-nut butter and honey sandwich in the morning, then spearfishing for 5 hours!! and only water during the day. usually after the first 1.5 hours my stomach settels and diving gets good, and my apnea times get better.
for statics try to eat a large dinner the day before, say Pasta and high carbs, then only water in the morning, avoid coffee and caffeinated beverages ect, and go for PB in the late mornings, after your stomach has processed all the food, but make sure to feed yourself well afterwards. Most importantly stay hydrated, and focus on complete exhalation to reduce your residual volume, and increase your vital capacity directly. If you use a lung expander you will see almost immediately, that you are most likely breathing with your chest, and not your diaphram, a lung expander will work the diaphram and with repeditive use you will be breathing correctly and deeply enough to surpass your PB.
good luck, and be safe.
TBGSUB.