How to choose media if you live in the Tropics

In Central America volcanoes and rivers are abundant, so finding lava rocks or river stones was the best way to fill our grow beds. The advantage of both media is that their pH is neutral, which will help to keep our system balanced.

When I was looking online for the size of rocks recommended (1/2” to 3/4” – about 2 cm), I started wondering why some lava rocks were red and others were black. It turns out that the red lava rocks used in the western world are processed (;, so I’m happy with the black natural volcanic rocks we found just up the street (available for free!).Lava rocks

When choosing a media, we considered the durability, weight, cost, plant holding, drainage, aeration, water retention, ease of handling and the lifespan. Lava rocks were the best option for us (only downside was the ease of handling) but worse comes to worse – we can always use some gloves. They are also lighter than the river rocks :)

 Side thoughts:

– I still don’t know if we should instal a bio filter to deal with the solid fish waste … Many people use a bucket filled with oyster shells – Maybe we could do the same with clam shells (which we can find on the beach we live on).

– pH and ammonia should be checked once a week – Nitrates should be checked once a month (more on this in the next post)

– Grow bed depth should not be less than 300 mm (12 inches)

See more about aquaponics in the tropics, Central America ->