Water change before adding fish, also low alk

[DEL 707]

My 56l tank has finally finished it's cycle. Ammonia and nitrites are down to 0, within 24 hours of dosing.
It's been like that for the last 2 days, I'm going to be a 30l water change on saturday and go get a fish, the 1st inhabitant in the tank.

I know I should be doing a big water change to lower nitrates. My red sea test kit is showing nitrates to be 50, that's as high as the kit goes.
Is one 30l water change going to be enough to lower nitrates that high?
Should I maybe do a water change on friday as well.

I've also been doing some other test, my PH is 7.8-8.0 and my alkalinity is 7dkh. Saltinity is 35ppt and I keep the temperature around 26°C
I'm using Red Sea Pro Coral salt and my numbers seem low compared to what it says on the tin. Do I have a problem?

Filtration in the tank is 7-8kg of dry rock. I also have a Fluval 107. I've removed a few of the sponges and replaced them with Seachem Matrix biomedia and carbon.
I've not turned the light on yet.

 

[gbroadbridge]

I know I should be doing a big water change to lower nitrates. My red sea test kit is showing nitrates to be 50, that's as high as the kit goes.
Is one 30l water change going to be enough to lower nitrates that high?
Should I maybe do a water change on friday as well.

A 30% water change will drop Nitrate by 30%.

50ppm Nitrate is no problem for fish so see what you have after the WC.

I've also been doing some other test, my PH is 7.8-8.0 and my alkalinity is 7dkh. Saltinity is 35ppt and I keep the temperature around 26°C
I'm using Red Sea Pro Coral salt and my numbers seem low compared to what it says on the tin. Do I have a problem?

An Alkalinity of 7 is close to Natural Sea water.
Ignore Alkalinity until you start to add coral - fish do not care.

Alk tends to swing around in new tanks - it's just not something to worry about at the moment.