75 Gallon Tank Help neglected aquarium fast: bring down nitrate

So I'm in a bit of a predicament. I've had this 300L Juwel Rio tank that I've been running for 4-5 years with the filter that it came with (and changing the different filter media sponges as instructed in the booklet). It has a Comet goldfish and a Common goldfish in (and they had been in a tiny 10 gallon with another Common for 3 years before that, but after that one died I insisted my parents buy me an appropriate sized aquarium).
And for 3 years everything went great, the odd algae bloom when there was too much sun in the room but all the levels were fine, the fish were healthy, I would do a 20% change every 2-4 weeks.

However last September I went off to college and left my mother in charge of my aquariums (I also have a 10 gallon planted with 2 cories). It's not her fault, she works full time, but she only changed the water twice in the year.
I was meant to come home twice for holidays but covid restrictions had me locked down in a different country.

So here I am back home and the nitrates are off the scale, and nitrite and ammonia are pretty high too (I'll test them again in the morning and update you with the exact numbers but I know they are very dangerous). Worst of all, my Comet goldfish Mendel, who I have had the longest, nearly 10 years, my first pet, is looking pretty rough: scales missing, lethargic, sitting on the bottom and not excited about food. (He is able to swim and I don't think he has swim bladder issues as he has had before).

I will change the water first thing tomorrow, but have been reading up on the best way to do this. My main question is:
Is it more dangerous to leave the nitrates high for longer or to shock the fish by doing a huge water change?

If someone could suggest a schedule for example 50%, then 20% the next day etc (whatever the numbers should be) I would greatly appreciate it as I really don't want to hurt my fish. I saw an article claiming I could do an 80% change if necessary but I'm doubtful of that.

My other issue is I only have a week before I have to go back to college. I will be back in 4 months and my dad has said he could step in and do a few changes between then, but I really want to get the levels back to normal before I leave.

And to hopefully delay this problem in the future I've ordered a fluval 407 external canister filter to add a lot more filtration to the system and hopefully stretch out time needed between water changes (I know water changes will still be necessary).

Sorry for the long slightly ranty post, I'm just really worried about my fish and angry at myself for making 2 people not interested in fish keeping take care of my aquariums.

 

personally I'd start with a large water change if the nitrates are off the charts and the ammonia and nitrites are present too. I think your fish would be better off that way, especially if you're about to move away for a while again - not a bad idea to give them a fresh start before then. I do large water changes (several times if need be) whenever my levels are off and my fish fare just fine.

 

The levels would be helpful but I agree, elevated ammonia and/or nitrite levels would likely present more of a health risk than any shock that might be experienced from an influx of clean water. If it's just high nitrates you could take a more conservative approach over a period of days.

 

I will go and get the levels in about 7 hours but the strips I used (imprecise I know) showed the nitrites more elevated than I've ever seen. When you say large water change what rough proportions are we talking about? More than half?

 

I would change whatever it takes initially to get ammonia & nitrites to relatively safe levels (below 0.5ppm). However, their presence indicates that something else is wrong and they shouldn’t be elevated even with high nitrates in the absence of water changes. It’s possible that the filter(s) are clogged or otherwise not functioning properly so check and clean (rinse not replace) the media, hoses/outlets etc when you do the water change.

 

Since you don't know the number, start with roughly 70%. A 50% water change will remove about 50% of the nitrates, so that may not be enough. On top of that, clean out the filter media in old tank water and do some gravel vacuuming if possible. Keep doing large water changes everyday, and definitely get your hands on a liquid teest kit if you can. Try some veggies soaked in garlic for your goldie, the garlic is good for their immune system and it'll also make the food more appealing

best of luck!

 

I will go and get the levels in about 7 hours but the strips I used (imprecise I know) showed the nitrites more elevated than I've ever seen. When you say large water change what rough proportions are we talking about? More than half?

I guess it just depends on your levels. The goal is to get them as low as you can, so as much as you can, squeeze the filter in the old water. If it were me, at least 75% then test and wait a few hours and test again and change again if need be if you don't want to do too much in too little time.

 

This is a special situation and requires some different thinking.

It is going to shock the fish if you change to fresh water in a hurry. The good bacteria are also in danger if you suddenly start cleaning everything. There is only enough bacteria in the 75 for the daily poop load.

I would suggest the fish are tolerating the situation today.
If it was my tank I would be changing small amounts of water multiple times each day for a week. I DEFINITELY would not be cleaning the filter or touching the gravel just yet. Slowly slowly is the way to bring this tank back .

I would suggest a 20% water change every 4 hours . Yes that’s three times a day. No cleaning of the gravel or filter. Do not clean all the glass.

Each day it would be safe to clean just some gravel at first . How much cleaning I can’t say , but take your time so you don’t kill all the bacteria.


I can almost guarantee if you clean everything and add fresh water the cycle will crash. Even the bacteria are used to living in a soup of nitrates.

 

A huge water change with a drip system is the best solution. And stop feeding the tank.

 

Here are the levels:
Nitrite: 0 mg/L
Nitrate: 250 mg/L
pH: 7.0
Chlorine: 0 mg/L

I guess the strips were malfunctioning about the nitrite, I'm so glad the bacteria is still working I was very worried the cycle had crashed.

I'm about to do a 1/3 water change, and change out the chemical filtration media (not touching the filter sponges or biological media for now).

For those mentioning gravel, I removed almost all of it a few years ago cause it trapped so much debris. There's a little left for them to forage around but it's mostly bare bottomed.

And I haven't fed the goldies today they're very mad at me

 

After doing a 50% water change (I added the fresh water back slowly over 2 hours, 1 bucket at a time) the levels are now:
Nitrite: 0.1 mg/L
Nitrate: 230 mg/L
pH: 7.6
Chlorine 0.1 mg/L

Is that pH swing big enough to worry about?
I added API Stress+ as I always do to condition the water so I guess the chlorine is still being taken out and not something to obsess over.
Could disturbing some of the decorations have released some nitrite build up somewhere where there wasn't bacteria?
Finally the nitrate. Given that 250mg/L is the max value of the test I'm pretty sure it was a lot higher than that so I'm glad it's now at a measurable amount.
Should I keep doing 50% water changes once a day or more like 20% 3 times a day as was suggested above?

 

Hi again Katsfish
A swing of .6 PH is of concern but hopefully not deadly.
I have been told a swing of 1.0 within 24 hours kills (angle fish ) some species. A swing of 1.0 is double what you have now.
Be aware the fish are already compromised / under stress from the state of the water as it was.

I don’t claim to have all the answers but continue to suggest you move slowly with any more changes to the water.
Perhaps smaller changes of water with more time between them?
Perhaps just one small water change each day?

 

Hi again Katsfish
A swing of .6 PH is of concern but hopefully not deadly.
I have been told a swing of 1.0 within 24 hours kills (angle fish ) some species. A swing of 1.0 is double what you have now.
Be aware the fish are already compromised / under stress from the state of the water as it was.

I don’t claim to have all the answers but continue to suggest you move slowly with any more changes to the water.
Perhaps smaller changes of water with more time between them?
Perhaps just one small water change each day?

Ah ok I wasn't sure about the pH. And I'm stumped as to why it has changed given it was 7 before the change and my tap water tested as 7 as well...
I'll slow down and do 20% a day then. But I do need to get it to completely safe levels by Monday. I'm just glad that the fish are actually swimming around now an hour later. I hope they're feeling at least a little better poor things

 

Unless you can get someone to do weekly water changes on the fish, and 1-2 feeds a day, it would be in the fishes best interest to be rehomed. With how everything is now, the fish are not likely to survive another year of that.

It is also not fair for you to expect your parents to take care of your pets when collage was more important to you. Goldfish are a 20+ year responsibility.

I would deeply consider finding them a new home for them. There are a lot of people who would love them and give them the adequate care they need.

 

I cases like this I recommend building up to the big water change gradually. I recommend you change 20% on day one, 25% on day two, 30% the next and so on until you are up to a 50% water change. Your fish have very gradually gotten acclimated to the parameters of the water. If you change them too quickly it can affect the fish and in some cases it has actually killed fish.

Since you only have a week to get this done I can suggest another way. Move the fish to another appropriate size container filled abut 1/3 full with water from the tank. Finish filling the container by dripping the fresh water in. Use a piece of airline tubing to drip the water in. You could just tie a knot in it to control the size of the drops or do what I do and put a control valve on the container end of the tubing. By doing this the fish will very slowly get acclimated to the fresh water.

Depending on the size of the container it could take several hours to fill the container. While this is happening go ahead and do your big water changes on the big tank. It may take several 50/75% water changes to get the nitrates down to a safe level. If the nitrates aren't down close to the same level in container as in the tank remove some water and drip more in. They should be pretty close though.

 

Do you have access to API Nitra-zorb? Get 2 size 6 pouches and that will reduce nitrates. It needs continued maintenance though. It is, however, simple...

 

Oh forgot to mention, if water changes lead to a drastic increase in pH then it can actually quickly kill the fish due to increased toxicity of ammonia.