With the purchase of our very rural home 2 years ago, we inherited a stable, mature koi / goldfish pond with 5 fish. The pond is ~350 gallons and has vigorous mechanical filtration. The previous owners *never* did water chemistries; always fed a "cheap", off-brand food (incl. feeding regular, non-wheat germ food in spring & fall), or used a winter pond de-icer.
There have been no issues until 1 month ago (4/25), when 1 of the goldfish (~18 years old) suddenly died. There was no warning other than possible lack of interest in feeding all spring by the 3 goldfish, but it has been cold; "she" had seemed normally active and had no obvious body lesions. We and the local pond / fish store attributed the death to old age -- until 3 days ago (5/22), when a 2nd goldfish (also ~18 years old) was found dead, and the 3rd goldfish (also ~18 years old) had simultaneously become very lethargic. The previous night we had noticed the 10 year old koi repeatedly flashing and breaching, but all else seemed well other than ongoing lack of interest in food by the 2 remaining goldfish.
In the absence of a definitive diagnosis, MICROBE-LIFT/BSDT (broad spectrum malachite green and formalin) was started empirically immediately on 5/22, following a 50% water change. We have been unable to find any treatment protocols either online or in koi books for MICROBE-LIFT'S use, other than the limited directions on the bottle. So, we have been doing 30-50% water changes every 8-14 hours then adding MICROBE-LIFT, dosage titrated to our pond size. I just put our pond heater (de-icer) back in after learning that increasing the water temp might be helpful in boosting their immune system.
Today is Day 3 (5/26). While there have been no more deaths, the remaining 4 fish (3 of which are koi) remain lethargic. They have absolutely no interest in feeding. The remaining 18-y.o. goldfish continues to segregate herself from the "herd" and is basically motionless; fins clamped, and resting near the pond bottom for hours at a time. None have any visible lesions, "pineconeing", or other abnormalities other than the goldfish, which developed hemorrhages of the tail veins ("injection") soon after becoming ill.
I have no access to a microscope. The local commercial koi dealer has not responded to our phone call, phone message, or text -- and not a soul was around their premises when we made a personal visit on 5/22 during their advertised business hours. (However, their tanks were actively running and contained hundreds of koi, so they are obviously still in business). The local pond / hobbyist koi shop confirmed the accuracy of my chemistries but was able to give no other guidance -- so I am turning to you for help.
Pond parameters:
~350 gallons. Well water, non-chlorinated.
Vigorous mechanical filtration, with a double waterfall.
Mechanical filter pads cleaned (thoroughly rinsed) ~1 x week in warm weather.
Water remains very clear.
Water hycinath (4 small plants) reintroduced 3 weeks ago, as usual every late spring. This was 1 week after the death of the first goldfish.
Hikari Gold food re-started ~7 weeks ago, after pond temps above 52F.
ALGAEFIX dosed once approx. 7 days prior to the first death (4/25). I have used it sparing in the past during warmer weather with no apparent ill-effects, and none seemed to occur this time either.
Chemistries have remained very stable and within normal limits:
Ammonia 0.25 (both before and after MICROBE-LIFT, which I understand increases ammonia temporarily)
Phosphate 2.0
pH 6.0-7.5 (the latest is 7.5)
Nitrite 0
I have many questions, but for starters:
1) What is the empiric treatment protocol for MICROBE-LIFT, in the absence of a definitive diagnosis?
2) How many days should MICROBE-LIFT be continued? How frequently should it be administered? How soon should health improvement be reasonably expected - hours, days, or weeks?
3) Could the MICROBE-LIFT be causing the 3 koi to be lethargic and anorexic? The 10 year-old koi's flashing & breaching stopped immediately after stopping MICROBE-LIFT. I'm wondering if this is because MICRO-LIFT is addressing the underlying issue -- or if the formalin/malachite green are toxic enough that the 10 year-old koi simply no longer has the energy to flash & breach. He (and the other 2 young koi) quit eating soon after MICROBE-LIFT was started -- again, I'm not sure if this is because of the medication or the underlying disease.
4) I'm considering salting as a next step. How soon after discontinuing MICROBE-LIFT can salting be started?
Thank you for bearing with this lengthy post. Any insights and guidance that you can give would be greatly appreciated.