Worm Casting Root Tabs
I have been using worm casting root tabs to help my trouble some R. macrandra. It seems like they appreciate the addition of rich substratum and I wanted to pass on this trick to other people having problems with rotala in general. I don't promise a panacea but it may help people turned off by osmocote tabs (I use both; osmocote where I tend to uproot plants and worm castings where I know they aren't moving anytime soon.)
Some features of worm castings:
1. Alive with bacteria and mycorhizzal fungi (not sure if all of them will survive underwater but I am sure some do as fungal cultures in lab grow in liquid media and they survive hypoxic conditions quite well)
2. Can be gotten as "organic".
3. Typically low soluble macronutrient concentration. The brand I use, "Wiggle Worms Castings" is 1-0-0.
4. Nitrogen is supplied mostly as insoluble nitrogen i.e ammonia sources. This means that you should see less of a spike in nutrient levels in combination with 3.
How to make them:
1. Mix a palmful of worm castings with 1 qt of aquarium water and mix well. Break up the chunks with a utensil or hand. The solution should be a slurry.
2. Wait overnight. You are giving a moment to reactivate dormant microbes and also to leach out highly soluble fractions of nutrients. You could in theory skip step 1 and 2 but these steps may help reduce excess nutrients and the staining of water.
3. Pour off the brown liquid after waiting overnight until you are left with a thick sludge. Feel free to pour off the less viscous sludge that sits on top as these are very fine particles that may cloud your water substantially if you disturb the substrate.
4. Scrape the wet sludge into a clay pot lined with a coffee filter.
5. Wait half a day (5+ hours) to let the water drain away so you are left with a thick cake, similar in texture to a wet dough or chocolate ganache.
6. Form this into your preferred shape. I recommend small sticks as my first batch of balls were difficult to insert into the substrate.
7. Sun dry until the outside is dry but you can tell the insides are still reasonably moist.
The resulting product is actually very durable yet still moist. It should be stable in water for many hours if not days (see picture of leftover balls in water). I think the worm mucous makes a good glue that holds everything together in water.
I'm sure you could amend this to include more nutrients but why bother? All we're essentially doing is putting soil into our tank in an easy to handle form.
Fluval Spec V
7x Microsynodontis sp (1)
1x Cranwelli Horned Frog