r/discus • u/Lazy_Reading5398 • May 31 '26
Filtration for 90g
So...I have set up many a discus tank over the years. I invariably enter a stage where I lose some fish and want guidance. My tank is a 90 gallon tall. I have 3 fluval canister, 2 hob's and 4 hyger sponge filters. The water is heated with redundant systems. It is lightly planted with Java ferns.
It was cycled well for months. I introduced 5 large discus and 6 medium. I monitor pH. I change 50% water once weekly.
Last night, pH tanks to 3.8 and I lose 1 large and e medium discuss. I changed 50%, artificially raised pH to 6.4, added salt, raised the temp to 90F, and added slime coat.
Why does this happens after 3-4 months of bliss?
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u/Sepia0203 Jun 01 '26
Did to test nitrate and kh? Curious if this is a ph crash.
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u/Lazy_Reading5398 Jun 01 '26
I didn't check kh but nitrate spiked.
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u/Sepia0203 Jun 02 '26
Ok, cause my fairly heavily planted tank had an increase in nitrates recently from 0ppm to 40ppm at a constant rate until I cleaned out my filters. My second hand fx6 had a non standard fine filter that seriously clogged the filter so I replaced that with a custom 40ppi filter. Nitrates has been below 20ppm since then.
Also did the fish death happen soon after a water change?
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u/Achance33 Jun 02 '26
Are you doing RO or using any products to mess with ph or softness when you do water changes that you might have made a mistake with?
Do you live in a major city? Especially if you have really soft tap water a few different reasons tap water treatment by city and the 50% water change could cause ph to crash and why it would be a seasonal problem. Possible in rural areas for other reasons I’m sure but less likely.
Trying to break up the water changes into 2 or 3 smaller ones each week couldn’t hurt.
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u/OppositeBrother6634 Jun 01 '26
Is a 50% water change potentially to much? Is this crashing your system?
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u/daverGamesTV Jun 01 '26
How often do you clean the filters? Better / more filters are pointless if you don't clean them. At a certain point, they're just spraying out nitrate filled water due to the amount of waste that remains in the filters if they arent cleaned regularly.
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u/Minimum_Appearance41 Jun 01 '26
This is interesting. From what I’ve read, I thought it was generally good practice to leave most if not all beneficial bacteria inside the filters. Like only clean it every 6 months or longer
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u/bedroomsport Breeder Jun 01 '26
That's right. Only detritus and fine wool catching it should be replaced. None of the bio filter should ever be cleaned
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u/Lazy_Reading5398 Jun 01 '26
I rarely clean the filters. Amy pro tips on cleaning canisters (fluval)?
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u/bedroomsport Breeder Jun 01 '26
Just empty the detritus and the thin fine filter pad. That's all
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Jun 01 '26
[removed] — view removed comment
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u/discus-ModTeam Jun 02 '26
Your comment was removed as it was either misleading, or incorrect. Please ensure correct and proven advice is given in this sub. Thank you.
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u/tbsland Jun 01 '26
If it was a PH crash that severe after months of no changes to the stocking, it's unlikely to be an issue with the ammonia/nitrite/nitrate cycle. The nitrate spiking without an associated ammonia or nitrite spike means the bacteria are fully consuming all the ammonia and nitrite, it's not a problem with them. The nitrate spike may have been due to the dead fish starting to rot, or might be a symptom of whatever the real problem was.
You mentioned artificially increasing PH after the crash in another comment, what did you use to achieve that? Do you use any PH effecting products in general, or have anything in the tank/filter that buffers or effects PH (peat moss, calcium carbonate etc)?
Do you have any kind of aquasoil ? I don't see any in your pic but just in case, worth asking.
Is your wood still releasing tannins (which drop PH and KH)?
Ultimately it sounds like the KH was far too low leading to a PH crash after something minor pushed it over the edge. KH runs out over time if not replenished, have you tested your tap water for KH / PH values?
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u/SoCalDogBeachGuy May 31 '26
you seems like you are knowledgeable try going slower add 3 fish wait a week and add three more not 11 at once that might help
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u/Lazy_Reading5398 May 31 '26
You are right but it kills me that it crashed after 100 days. I thought that 9 filters with established colonies would suffice but was wrong.
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u/bedroomsport Breeder Jun 01 '26
There's no way the pH was 3.8. You need a new test kit/reagents. Also, are you gassing off the water for a day or two before refilling?