water chemistry problems

[andyb]

sorry this is going to be a bit long winded. First of all i will give you as much info as pos, normal tank readings are
ammonia 0
nitrate 5
nitrite 0
ph 6.7
kh 3-4
gh 8
temp 29c
juwel 450 litre tank built in filter
discus 9 between 5- 7 inches, 6 tetras, 1 plec, 3 cory"s
tank established 14 months ago
use 80% RO, 20% tap water
gravel bottom, live plants.
Now onto the problem, 3 days ago i checked my water and the ammonia was 2.5, nitrate still 5, nitrite 0.25, ph still 6.7 but kh was almost 0.
changed a third of the water using 50% ro, 50% tap, but while i was doing that i checked the sponges in the filter the sponges that hold the bacteria look like new the bacteria has vanished.
did another third water change yesterday and today using 50-50 added live bacteria also treat tap water and ro
reading now ammonia 0.5, nitrate 5, nitrite still 0.25, ph still 6.7, still no kh.
discus ok i thought by adding more tap water the kh would rise a bit but its not
could the kh have something to do with the bacteria dying and how can i get around these problems.
any help please.

thanks Andy

[Jhhnn]

Seems odd, overall. Have you medicated the tank recently? Any possibility that cleaning agents may have contaminated it?

It may have something to do with it being a planted tank- out of my realm- so reposting under the planted tank category might be helpful...

[andyb]

thanks Jhhnn,
no medication got a hospital tank for that. Ammonia gone now, Nitrite still 0.2.
put marine salt in thinking that might work, PH went from 6.7 to 7.2, Gh 8 to 12, but kh still 1 weird. Tap water kh is 8 mixing 50-50 RO and tap would have worked.

[Willie]

The biochemistry of ammonia conversion to nitrate is such that nitrite cannot accumulate unless your cycle is broken. (Conversion of ammonia to nitrite is slow, conversion of nitrite to nitrate is very fast.)

The bacteria in your system is extremely resilient, very tough to kill without using wide spectrum antibiotics. If possible, trade a sponge with a fellow aquarist and reseed your system.

Good luck, Willie

[Jhhnn]

Have you actually checked the KH of the tapwater? I haven't actually checked mine for many months... we all make assumptions, sometimes they're inaccurate... If it's changed for some reason, gone down, that would explain the low readings... How old is the testkit? They can lose accuracy w/ age, iirc... Adding baking soda to the fill water will raise the KH, and the pH, too, if only a little.

I really can't explain the loss of the bio, however... but it seems as if you've caught the problem in time, so staying on top of it while figuring it out looks like a good course of action.

Like I offered earlier, maybe the planted tank afficiandos can offer greater insight...

[andyb]

thanks for the info, tap KH is 8, will try planted post. At least all my discus are healthy. Going to change 33% of the water tomorrow, as before 50% RO, 50% tap.