How do I lower my KH? AKA, Eco-Complete is driving me crazy!

Hmmmm. I bought about 10 bags of Eco Complete to use on my 180g tank. When I first got it I had the same issues with KH elevation, but no to the same extent. I pulled out some of the substrate and inspected it closely. There were little bits of white flecks in it. A few drops of concentrated hydrochloric acid confirmed that the bits were in fact small pieces of seashell.

I also contacted CaribSea about it and they told me they had some issues with cross-contamination from their marine substrates. They offered to replace the entire batch for me. I elected to stick it out since changing things out at that point would have been a huge project.

The KH elevation persisted for about 6 months. Doing lots of WC's (I did 50% per week) and running high CO2 levels will deplete the CaCO3 over time. At this point I'm growing toninas just fine and I'm supplementing with NaHCO3 at each waterchange to maintain a KH of 3.

Niko's recommendation to switch to aquasoil would be shared by many people. Their consistency and quality control is probably the best on the market. The stuff works great too, but don't be led to believe that it's the only way to grow plants.

If I re-did the 180g tank I'd probably use Aaron's technique of a mineralized substrate, but I'd try it in something smaller first.

If you decide to stick it out, please let us know how long the buffering effect lasts. I'd to curious to compare it with my own experience.

BryceM - After reading your post, i pulled out the KH test kit again and re-tested my 24 gallon, and was a little surprised to see you were right - my KH was 3. Last time I tested a couple months ago it was 14. I'm guessing this corresponds with the great growth I seen recently in that tank from certain plants. Pogostemon Helferi has taken off, and this plant struggled for months before recently carpeting (literally) my foreground. This is heartening, and is enough to keep me from swapping out the substrate in the small tank as well. I wish I had kept a journal of test results so I could graph the decline.

Niko - My plants aren't doing great, so I do feel like I'm trying to chase down the reason. I think I've eliminated most other causes. I dialed down light, introduced a balanced, regular fert schedule, and increased my co2 and water circulation.
I agree 100% that using the eco-complete was a great learning tool - I feel like I was a little handicapped with the Eco from the beginning, which pushed me to really focus on learning how to read the plants, instead of test kits. However... I really look forward to trying AS with my next tank. I have great, clean water out of the tap, and it would be nice to have a substrate that didn't negate that.

Thank you both for the replies.