Organic latent (uneaten foods and fish waste) waters create conditions
that encourage disease, parasites, and opportunistic bacteria, besides
the build-up of DOCs, which by the way, adds to the TDS level. NitrAte
levels can get quite high. As these organics decay, they use a lot of
oxygen - the process is called eutrophication. The same thing happens
within your filter if you don't pre-filter, or clean the intrapment
media - the filter itself becomes the source of organic pollution! It
also enhances conversion of nitrAte to nitrite. Docs (dissolved organic
compounds) inhibit nitrification and increase BOD (bio-chemical oxygen
demand) - high BOD reduces amount of oxygen in tank. DOCs are not
detected by a hardness test, however they will measure on a
conductivity meter. By comparing the differences between the two test
you can determine DOC levels. DOCs become part of the TDS reading -
while the TDS value may very slighty, it must be maintained within a
nerrow range (slowly increased or decreased - 20%) - thus, a water
change of no more than 20% on a tank with little or no
maintenance......
The symptoms you gave don't add up to Flex. disease - no white fuzzy
lesions of the mouth or white fuzzy patches scattered over the body! I
would suspect another gram-negative bacterium called Aeromonas - fits
your symptoms better - a secondary bacterial infection as is Flex.
Treated the same as you would treat Flex. disease, sometimes infects at
the same time as Flex. Feeding a medicated food along with adding an
antibiotic to the tank is the best treatment. Tetra's medicated foods
don't work on Flex. disease - get a Waterlife product called Protozin
and Myxazin (medicated food). For treating the tank, Potassium
Permanganate works, 1/2 tsp. per 10 gals, but takes longer than
Maracyn-Two or Kanamycin. Oxytetracycline, Erythromycin or Enrofloxacin
(baytril) are faster but they would also knock out your
bio-filter......
You say your water parameters/quality is good - your temp. got to high,
tanks substrate dirty, and you did a 100% water change in two days - a
bit of fluctuation going on there. Here is the five points of defining
water quality; #1 - organic pollution, #2 - ammonia, nitrite and
nitrAte, #3 - dH, pH, temperature. #4 chemically clean, ie; chlorine,
heavy metals, treatment chemicals, organophosphates, #5 -
***stability***, not fluctuation............ Frank