Nitrate problems

Hi, I recently purchased a used cichlid tank set-up complete with fish. I am new to cichlid keeping but have had a koi pond for over a decade.
I transported about 25% of the original water and topped that up with warm treated tap water. I didn't originally clean the substrate which was pretty dirty but have since syphoned it twice. I have been doing daily water checks and whilst my levels are generally ok/good the nitrates are very high, at least 80ppm.
Nitrite has been 0ppm for days and has never been high. Ammonia did hit 1.0ppm but is now back down to 0ppm. I did a 25% water change a couple of days ago and then another 40% yesterday and added double the recommended dose of Seachem Prime each time but the nitrate doesn't seem to be going down.
The fish on the whole seem ok and feeding well although a couple are a bit nervous but i figured that have only just been moved about.
Other than continuing to do daily water changes is there anything else i should be doing? Any help would be greatly appreciated.
I transported about 25% of the original water and topped that up with warm treated tap water. I didn't originally clean the substrate which was pretty dirty but have since syphoned it twice. I have been doing daily water checks and whilst my levels are generally ok/good the nitrates are very high, at least 80ppm.
Nitrite has been 0ppm for days and has never been high. Ammonia did hit 1.0ppm but is now back down to 0ppm. I did a 25% water change a couple of days ago and then another 40% yesterday and added double the recommended dose of Seachem Prime each time but the nitrate doesn't seem to be going down.
The fish on the whole seem ok and feeding well although a couple are a bit nervous but i figured that have only just been moved about.
Other than continuing to do daily water changes is there anything else i should be doing? Any help would be greatly appreciated.