The custom micro mix thread has reached nearly 100 pages and nearly 1,500 posts. Additionally, the old threads on trace toxicity are long and full of chaff. Now, I try not to be lazy and generally am willing to put some time into researching a topic, but this is a bit much. I realized I'm probably not the only one getting overwhelmed. Could someone give a summary of what we currently know about micro dosing, in particular:
1. Is micro toxicity a thing? Are there certain nutrients that we can lard on without a problem and others that we have to watch out for? "Toxicity" term is debatable, but I along with some other experienced members of the forum (burr740, saxa tilly) have observed problems of using too many traces, particularly the CSM+B blend. Most common problem is stunted, shriveled tips in plants like Alternanthera Reineckii, Ludwigia Glandulosa, and some rotala/lythraceae. I managed to fry a swordplant with high doses of CSM+B, O+ tabs, and unknown tap water parameters.
2. What is the difference between the various chelators? Do those differences really matter? Does the buildup of chelators cause harm? Is there a problem with using multiple chelators in the same tank? Chelators become unstable at various pH levels, and these are believed to be part of the problem. Unstable chelators can possibly bind or interfere with calcium uptake or maybe other nutrients. The symptom usually looks like calcium deficiency though. EDTA becomes unstable (detaches from iron?) at lower pH than DPTA, and EDTA is what is used with CSM+B. So CSM+B can be a problem when pH is routinely over 7.0, for example. I think pH 6.5 and under is the EDTA recommendation - feel free to look the specific values up. I'm just going from memory here.
3. How do you identify micro toxicities or deficiencies? It's tough, because the symptoms can look the same. And CO2 issues also manifest themselves as stunted, curled tips. Always check and double-check CO2 first, along with light levels. Symptoms will usually be curled, burned, stunted tips in plants like AR. If you have this, plus no other real algae issues like BBA, OK growth in other plants, good pH drop and flow, and using CSM+B or EDTA chelators at EI or higher levels, it's beneficial to try another trace mix or lower the CSM+B dosing. Burr740 and I were doing CSM+B at around 0.015 ppm Fe three times a week - with some DPTA iron added in. Very low compared to EI. Until a few years ago, the EI guidance was up to 0.5 ppm Fe 2-3 times a week, and some people were dosing that much CSM+B. Now the EI recommendations are at the 0.2 ppm Fe level. Inert substrates and softer water (GH) make it more likely to see issues.
4. Tap water and soil usually have some nutrients. If you have a low-light tank, especially a dirt tank, do you still need to add micros? Does fish food have enough micros to have an effect? Do "shrimp blocks" give off anything useful to plants? Low light with dirt may need some traces added, but you could easily get by with low levels that would never risk toxicity. Can't say if tap and fish food would be enough.
5. Is CSM+B a good or bad micro mix? How does it compare to other micro mixes? Many people, including me, have used it and grown great plants with nice tanks. But, I have overused it and saw stunting in AR and Ludwigia Glandulosa in particular. Most plants like vals, crypts, other ludwigias had no issues with higher CSM+B levels. If you do use it, be wary of pH, and you will need less of it than another trace mix that uses SO4-based compounds. 0.015 ppm Fe 3x per week will probably be enough with inert substrate, and consider adding extra iron in an equal amount.
6. Iron is usually grouped with micros. How much iron do we really need to add? Does the source matter? Is it better to add iron to the water or have it in the substrate? I've always added it into the water (except for some O+ tabs that have it). Above I listed a good CSM+B starting point for dosing. For my trace mix with DPTA iron and SO4 traces I have used 0.3 to 0.7 ppm Fe weekly, with inert sand substrate. Some go higher, some lower. Good starting point is 0.15 ppm Fe 3x per week and go from there.
7. How important are nutrient ratios? Which ones do we really need to worry about? Not just between different micronutrients but also between micros and macros. For micros, one to watch is the Fe:Mn ratio. Burr was seeing issues at a 2:1 ratio, and from his experimentation a 3:1 to 5:1 ratio works much better. Higher boron levels might also cause problems, but if you use it in ratios recommended in the custom micro thread you should be fine -s omething like 0.03-0.04 ppm B in a dose of 0.15 ppm Fe. I have read a little about Ca - Mg - K ratios, where high K can cause issues with Mg uptake. I noticed it in moneywort when K:Mg was over 4:1, but that was the only plant. I've browsed around some German forums and many of them keep K fairly low compared to a lot of the people on this forum. I've also had tap water that was around 1:1 Ca and Mg, and things always went better when I added extra calcium for at least a 2:1 ratio. Theoretically there shouldn't be a Ca deficiency at 15 ppm, but I noticed improvement when I raised it to 30-35 ppm. If you think you have a ratio imbalance, post your parameters and issues to the forum and let people help. It's down on the list of things to check though, after CO2/light balance, flow, cleanliness, biomass, light period etc.
8. Can dosing or overdosing micros be beneficial or harmful to fish or inverts? Don't really know. I think copper can be lethal, but those levels are much higher than you would ever see dosing something like 0.002 ppm Cu three times a week. Copper pipes in the house might also contribute some copper.
9. Keeping in mind that plant species have different preferences, and as aquarists we're better off striving for "good enough" than "ideal", in general, what dose should we use for each micronutrient? Here is the latest recipe from Burr - ratios are 0.15 ppm Fe, but doses can be smaller, like 0.1 ppm Fe three times a week:
Fe - .15 (he uses combination of DPTA and gluconate; I have never tried gluconate)
Mn - .045
B - .037
Zn - .035
Cu - .0025
Mo - .0013
Ni - .0003
10. Is there anything else we should know about dosing micronutrients? Lots of people have had great success with the SO4-based mixes, and people are selling them pre-made on this forum. I'd recommend going with those at this point. Don't get crazy with micros and you should be fine. Any issues you have will almost certainly be something else.
It's okay if you can only answer one or two questions. I just think the topic has grown to the point that having all the info consolidated in one thread would be helpful. Since this is also meant to help newbies, please try to keep your explanations in layman's terms. If you know of a good explanation elsewhere on the forum, please paste or quote it here or link to a particular post. It's very frustrating to sift through a dozen-page thread for a single answer or to have to go through a dozen threads on the same topic, each with only one or two pieces of the puzzle.