Don't put anything in the lagoon that you haven't already eaten. Minimize household chemicals, bleach, etc.
The house I grew up in had a lagoon for about 60 years. In the early 60's the town ran a sewer line down the road & encouraged everyone to hook up. It ran straight into a nearby brook. In the 80's the town paid to put in septic systems for everyone to get them off the sewer line. I think all in all that the lagoon was as good as anything. Didn't smell unless you were close enopugh to fall in. Grass grew real good around it, but it didn't get mowed. MikeD74T