Excel / glutaraldehyde decomposition mechanisms and impact to automatic dosing

Hi experts,


I've been running happily with my non-CO2 cold water tank for about 9 months, and was looking for a small bump in plant growth rate without the cost and extra maintenance of CO2. I started dosing Excel and was pleased with the results, just enough growth to recover from occasional damage and keep the plants visibly growign without inducing a lot of additional weekly maintenance. This is all just context for my question. While the Excel is working for me, I have frequent business trips away from home and a busy schedule so the daily manual doses would be erratic if not automated. To solve this I built an automated Arduino-based pump and light controller to dose teh Excel daily each morning (uses a peristaltic pump) and control the lights. Its all working great, but I wonder about whether the Excel will remain stable/active in the tubing of the dosing system.


I've read both on Seachem website as well as this forum and others that the Excel doses somehow break down over the course of a day which drives the need to dose daily. But I haven't found much information on what causes the decomposition. On some forums I've seen hobbyists claim that light causes it, but looking up some documentation from chemical suppliers on glutaraldehyde storage and transportation i see no mention of protection against light. Presumably the stuff in the bottle stays stable and active, only after diluting it in the tank does it start to break down, or maybe it just gets consumed? In my dosing pump system and tank size (20 gal nominal but only 15 gal of actual water, Excel doses are ~1.5ml/day) there's about a week's worth of doses stored within the tubing which is translucent food-grade silicone. While I am getting some smaller-ID tubing to reduce this volume, I'll still have at least a couple days' doses stored in the tubing. I'd like to be sure I am dosing a controlled amount of the chemical, not some uncontrolled partially-deactivated variant of it. Does anyone have authoritative information on what causes the Excel dose to last ~1 day (just consumption by plants, or deactivation/decomposition by what mechanisms) and whether that mechanism will impact automatic pump-based dosing. Also is it safe to dilute the Excel so that it can be pumped through the tubing faster and what solvent is appropriate (I assume DI water?). I've emailed this question to SeaChem but haven't gotten any response.


thanks!


Mike

 

I just got a response from Seachem and thought others might find the info useful so I'll post it here:

 

Thanks Tom, that article was quite helpful. (Being an electrical engineer by training not a biologist or chemist I had to read it a few times). My main takeaways were that in water from a real habitat, biological metabolism consumes glutaraldehyde at about the rate claimed by Seachem, while sterile solutions in the dark decompose much more slowly. It was interesting to see that the whole metabolism cycle took ~2-3 days to fully complete through several stages and intermediate compounds eventually getting to CO2