How much is too much water to change - end of cycle

[Jabes]

Hi,

I am a newbie fishkeeper. Well, no fish yet! I have been following the fishlabs fish-out cycle instructions (basically adding ammonia each day and waiting for the bacteria to form). Three weeks in and the ammonia is being converted overnight, and the nitrites too.
We have been checking daily with API liquid test kit.
We were about to buy our fish (tomorrow) but I have been suspicious of my low nitrates so bough a new test kit (NT labs), and it shows we actually have quite high nitrates - which is more in line with what I would have expected to be honest (we have done a couple of 20% water changes on the way through).
A quick google shows sometimes you have to really smash around the API bottle no. 2 to get the chemical properly in suspension - now I've done that it is now reading 80+ so obviously a few more water changes needed to get the water chemistry low enough for new fish.
If I do a 25% water change a few times with a few hours in between will my bacteria survive? Would really like to get the fish tomorrow, daughter has been waiting patiently for weeks

 

[HoldenOn]

Hi,

I am a newbie fishkeeper. Well, no fish yet! I have been following the fishlabs fish-out cycle instructions (basically adding ammonia each day and waiting for the bacteria to form). Three weeks in and the ammonia is being converted overnight, and the nitrites too.
We have been checking daily with API liquid test kit.
We were about to buy our fish (tomorrow) but I have been suspicious of my low nitrates so bough a new test kit (NT labs), and it shows we actually have quite high nitrates - which is more in line with what I would have expected to be honest (we have done a couple of 20% water changes on the way through).
A quick google shows sometimes you have to really smash around the API bottle no. 2 to get the chemical properly in suspension - now I've done that it is now reading 80+ so obviously a few more water changes needed to get the water chemistry low enough for new fish.
If I do a 25% water change a few times with a few hours in between will my bacteria survive? Would really like to get the fish tomorrow, daughter has been waiting patiently for weeks

As long as you are using a dechlorinator you should be fine doing a big 50% twice. @essjay knows more about this than I do.

 

[Essjay]

You can change just about all the water at one go. The bacteria you have so patiently grown live on surfaces not in the water. As HoldenOn said, make sure you add dechlorinator, and warm the water to roughly the temperature the fish need, and the heater will do the rest if you do the water change today and go shopping tomorrow.

 

[Jabes]

Super... I had done two 25% water changes earlier; now I've just done a 50%.
I'll test it again in a second. The API test (now I have it working) seems higher than the NT Labs one -- since we've been using the API Labs test for about three weeks without having shaken bottle 2 properly, I suspect that the chemical in suspension is now too concentrated and may be over-reading and that I should just trust the NT Labs test and ignore the API nitrate results now. Thoughts?

Best wishes
James

 

[Essjay]

If you change all the water right down to the substrate that will get the nitrate down to tap water level.

Say your tank nitrate was 100 ppm and you tap nitrate was zero (just to make the calculation easier)
The first 25% water change removed 25 ppm leaving 75 ppm in the tank.
The second 25% water change removed 18.75 ppm leaving 56.25 ppm in the tank.
The 50% water change removed 28 ppm leaving 28 ppm still in the tank.

A 100% water would drop the tank nitrate to zero.

 

[Jabes]

I understand the dilution effect. I've done two 50%'s changes now.
The NT Labs test tube tester is showing near zero, but the API tester is 40+. I think the API tester is now broken because we used solution 2 for 20 odd tests without having shaken it up - so the suspension in there must now be of greater strength than intended.

I also have maidenhead aquatics and the API test strips both of which are showing higher readings than the liquid NT labs (but under 40), .. but everything I've read says these are nowhere near as reliable as the liquid testers.

I think that I've done enough and we're now all set to go unless you tell me different!

 

[Essjay]

Ah, if you've done so many tests with the API tester you will have changed the relative concentrations of the ingredients. I hadn't realised you'd done so many. The equivalent bottle with the NT Labs tester is a powder, isn't it? So no shaking of the bottle involved, just the test tube.

One thing you can do is look up your water quality report on your water company's website and look for nitrate. Then test your tap water and see which tester agrees with the mean nitrate value in the water quality report.

While you are on the website, do a search for your water hardness as well - hardness in important to fish and we need to keep fish which come from roughly the same hardness as our tap water.