What substrate tabs are you using now - I may have some insight on that. Also, I didn't catch the GH of your source or tank water.Terrafox wrote: ↑Thu Apr 03, 2025 6:05 am I had a similar issue in my 65-gallon tank recently, and it boiled down to water flow. The fertilizer nutrients just weren't being circulated effectively around the plants.
I've since adjusted the setup - the filter outlet is now a spray bar, and I've added a power head just beneath the water's surface, directing the flow parallel to the surface, from back to front. This creates a circulation pattern where the water flows down the front glass, along the substrate, and then back up the rear glass, where there's a low-pressure area. This change has largely resolved my issue, and my plants are now growing much better.
You mentioned having a powerhead in the past, but it was too strong for your fish and you were concerned about breaking the surface and losing CO2. I can see why you'd think that, but strong currents aren't ideal for Echinodorus, and they can actually move nutrients past the plant's leaves before they can be absorbed. I've had some experience with this myself - I lost a couple of plants due to strong currents from my canister filter, but moving them to a different spot helped them recover.
Regarding surface disturbance, it's a bit of a debated topic these days. While it's true that more vigorous disturbance can increase gas exchange, I aim for some gentle rippling at the filter return, just not excessive and confined to a small area. You're working with low-tech methods, and that's what I use too - high-tech is a whole different story.
As for injecting CO2, I don't think that's the answer. There's usually enough CO2 produced by decomposition in the substrate to get the job done. However, your 10-hour light cycle is likely too long and needs to be balanced. Try reducing it to 8 hours, and be prepared to go down to 7 hours if needed. It takes a couple of weeks for changes to become noticeable, so be patient.
To give you an idea of what I'm suggesting, I've had success with moderate light on 7 hours, using Flourish Tabs next to my larger swords and replacing them every 3 months. I also dose Flourish Comprehensive Supplement once a week, on the day after my water change, at the recommended single dose level. No CO2 needed.