Simply Koi and More Koi

Morning all. I found Costia on a few of my fish last week and treated with MG/F (1%/30% w/v, 2 doses over five days) which has done a great job on the wee beasties but I've had a massive increase in my NH3 from the normal 0.02ppm average to something like 2.4 today!!! Now, the fish look ok for the time being. In search of a reason to explain the Ammo spike I reached (as usual) for Duncan's SbSAKD&T book and, as I understand it, I read that formalin binds with NH3 and makes readings unreliable (that bit I can confirm - 2.4 on the Hanna meter, and zero on my drop test kit (?)).

My question is in two parts really; 1, have I understood Dunc's book correctly and despite the outrageous NH3 reading trust that the formalin has it under wraps and it will return to normal in due course; and 2, how long is that period of "due course" likely to take?

If I've totally got the wrong end of the stick I'll be doing a big water change tonight and trying to figure out what I've done to kill off my filter (poxy two chamber brushes + jap mat/fine filter foam augmented by small veggie bed/stream and an additional 18x biocenois baskets (12"x12") placed in the main pond to mature prior to AFS completion) - because I haven't done anything unusual except add the (carefully measured dose of) MGF. Ordinarily I don't have any issues with ammonia, it's pH I have to watch carefully even with Kh at 6 to 8 and regular doses of Sodium Bicarb to maintain it.

Thanks as always, Mick

Nick,

The Hanna, in common with other electronic test equipment, uses a test method called the Nessler method (increasingly deep shades of yellow as the ammonia level increases) and this method cannot distinguish between ammonia and aldehydes. Formalin is made from formaldehyde which is obviously an aldehyde so we cannot use the Nessler method until all traces of the formalin have gone because it will give false high readings.

Most manual kits use a test method called the Salicylate method (increasingly darker shades of green with increasing ammonia levels) which isn't affected by aldehydes. They may not be as accurate but they can be used to measure ammonia when formalin is present.

I can't give you an accurate forecast as to when all traces of the formalin and its breakdown products will be totally gone but, obviously, water changes after it has done its work will dilute it out of your system and you should trust the manual kit until then.

Phew for that! Thanks Syd, that puts my mind at rest - I'll monitor carefully. Best regards, M