I dose my big (55g) with a couple of dosing pumps, one for Traces and one for ferts. This is a minor problem for Traces, as they settle out and eventually clog up the tubing. I replaced the tubing the other day and turned the pump on to get the air out. Problem is that I forgot to turn it off again. I'm not sure how much was in the bottle, as it also gets clouded over. But it must have been at least half full, which equates to at least 5 grams of Traces or 5+ PPM of Iron in the tank. I noticed the pump was still running today when I did my WC and realized what had happened. Did the WC expecting the worst, but did not find any casualties, Shrimp or Snails. I tested the Iron today and it came out very close to zero. (I'll have to check the Test Kit)
I did have a lot of pruning to do though, the Ludwigia is growing like it used to and the Sword was taking over the tank again. I guess I'm not dosing enough Traces. :-)
One odd thing though, the Ammonia checker is reading at a low level, whereas it's normally zero?