There are many suitable substrates for growing marine plants in the aquarium. The composition, depth and size of the substrate used is largely based on the individual species of macro algae or sea grass desired. Many commercial products are available to hobbyists for use with marine plants, but most are marketed for the refugium. Although macro algae does not derive any nutrients directly form the substrate, with the exception of sea grass, some type of substrate is usually needed for most species so that they can readily attach themselves. By far, the most popular substrate is the use of a fine grade aragonite sand at varying depths of up to 6” or more. Fine grade sand is readily colonized by most all Caulerpa species and is generally the easiest to maintain. There are also proven benefits to providing a deep sand bed to reduce nitrates and to culture marine fauna, but macro algae only require about 1” or less to attach and grow. Sea grass, however, does require a deep sand bed as its root system can extend quite deep, as much as 12”.  

Aragonite SubstrateCareful attention should be taken to not introduce substrate to the aquarium that is too compacted, such as silica or quartz sand as this will most likely cause a dense anaerobic layer in the sand bed that can be toxic to tank inhabitants if disturbed. If a mixed macro algae and sea grass system is desired, it would need to devote some portion of the aquarium to a deep sand bed in order to successfully grow vascular plants. For the most part, a mixture of substrates will create an environment suitable for the addition of most any species desired. Most commonly available substrates are composed of variable amounts of aragonite and/or calcite. Aragonite is beneficial in its ability to properly buffer the aquarium water, helping to maintain both ph and alkalinity. Smaller grain sizes dissolve faster while coarse media such as crushed coral is much slower to break down requiring a higher ph to dissolve. Marine plants that do well in a fine to medium grade aragonite sand include most species of Caulerpa and calcified algae such as shaving brush & mermaids fan, as well as sea grass. 

Coarse media such as crushed coral, shell or live rock rubble can also be used to anchor marine plants and is a good choice if a deep sand bed is not needed, especially in the refugium. The only drawback to using coarse sand/rubble is that it tends to collect detritus and sediment, often becoming a nutrient trap over time. In marine plant dominated aquariums this can be an added benefit however, as high levels of nutrients are needed for long term success. Some invertebrates are better suited to this environment, such as amphipods, while other soft bodied invertebrates desire a less abrasive environment.

Coral Rubble SubstrateMost varieties of red and brown macro algae grow on rocks and hard bottom habitats in their natural environment, so a coarser substrate is more suited for anchoring. Marine macro algae such as Gracilaria, Botryolcadia, Sargassum and Halymenia can be glued or placed between rocks/rubble and will readily attach themselves. Most all macro algae are very adaptable, and will grow free floating or attach to most any surface, including substrate, live rock or even the sides or bottom of aquariums.

During the early 1990’s, mud filters began to gain in popularity for use in the refugium. Several manufacturers began offering a product that would duplicate tropical coastal environments, such as lagoons and mangrove habitats. These products claim to provide a variety of trace elements including, calcium, iodine, strontium, iron, and free carbon. The idea behind the “mud” was to provide a replenishing source of nutrients by slowly releasing them into the aquarium water. Below is a brief summary detailing the most popular aquarium mud, its composition and qualities.  

Miracle Mud

Manufactured by Ecosystems Aquarium Inc., this substrate is light tan in color with a wide range of grain sizes. The composition is very silty and must be topped with aragonite so as not to disturb the substrate. The manufacturer claims that this product contains over 68 naturally occuring elements. The replacement of approximately 50% of the substrate should be done every 12 months to maintain the slow release of nutrients.

Mineral Mud

Manufactured by CaribSea Inc., this substrate is a dark brown almost black mud which includes a mix of grain sizes including large chunks of sediment. This particular product is very silty and must be topped with aragonite or similar product to prevent it from clouding the aquarium water. The manufacturer claims that it contains simply "marine organics" created to mimic coastal marine environments.

Fiji Mud Refugium Booster

Manufactured by Walt Smith International Inc., this substrate is a wild collected organic mix harvested from Fiji. It is dark brown in composition and is designed to be topped with aragonite or similar product.  No ingredients are listed except that it is deep water mud from Fiji.


Manufactured by Marc Weiss. F.O.R.M (funky old reef mud) is actually a additive that is added to the refugium to release needed nutrients. This particular product is a dark rich highly organic material derived from the ferment of seaweed.

Marine Biosediment

Manufactured by Kent Marine Inc., this substrate is a fine aragonite based sand containing calcium, magnesium, strontium, potassium, carbonate, sulfate and other trace elements.

Some of the potential problems associated with the use of “mud” in an aquarium or refugium is that the sediment is very silty and can cloud up the water anytime the substrate is disturbed or new product is added. While the use of mud does provide a good growing medium for many macro algae, sea grass and mangroves, it is largely unknown how much of and at what rate trace elements are being introduced. Some hobbyists have introduced wild, highly organic mud from locally collected coastal sources into their refugium or planted tank. 

While this practice can be beneficial for growing sea grass, the contents of the substrate will vary considerably depending on where it is collected and the composition largely unknown. For this reason it is not really a good idea unless the contents have been properly identified or collected from a known, pristine habitat.  Some freshwater substrates formulated for growing tropical aquarium plants can offer similar results in heavily planted aquariums containing marine vascular plants and are often more affordable than many of the available marine products. 

Whatever substrate is used, it is important to note that the best results with growing algae and, more importantly sea grass, will be achieved with a properly aged and colonized sand bed. Stability is the key to long term success, so it is best to allow the maturing process to be begin in new systems by not disturbing the substrate or uprooting plants or changing the aquascape. A proper substrate for growing marine plants will require little maintenance once established and should be left alone for the most part.

Copyright 2010 GCE All rights reserved. No part of this online publication may be reproduced in any form by any means without the expressed permission of the author. All images are the property of Gulf Coast Ecosystems unless otherwise noted and should not be reproduced or distributed without permission. Selecting Quality Plants

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