EPA and DHA are found in the same algae. The younger you harvest the algae, the more EPA.
First of all please note that every individual responds differently to Omega-3 intake.
EPA and DHA mostly do different things. If your goal is reducing cellular inflammation, then you probably need more EPA. People who need to recover from depression, ADHD, brain trauma, etc. are advised to maintain high levels of EPA in the blood.
DHA does a great job of making membranes (especially those in the brain) a lot more fluid than EPA does. This increase in membrane fluidity is critical for synaptic vesicles and the retina of the eye. Nonetheless you always cover your bets with Omega-3 fatty acids by using both EPA and DHA at the same time.
More info can be found here: What health claims may Testa Omega-3 EPA + DHA make?