Goldie tank with high Nitrates

Question
Hi Dave,
I presently have 4 tanks but my question is about my Goldie tank which I've had set up for about 15 months.  I have 1 Ryukin and 1 Fan Tail in a 29 Gallon tank with an AquaClear70 filter.
I have battled with high Nitrate levels the whole time I've had my tank.  I thought I had it under control for a while when I broke up my weekly 30% water changes to 2 15% water changes per week because my Nitrate readings were around 10 instead of the usual 40 or 80 but when I was talking to the Aquarium place about getting a 50 to 65 gallon tank for my Goldies I was told to NEVER do 2 water changes a week so I stopped.  Well, my Nitrates are back up where they've always been and now I'm not sure what to do anymore.
I have never missed a weekly water change.  I vacuum my gravel once a month.  The filter media is rinsed in the water I remove from the tank and only replace one part of the 3 as needed (not monthly).  I clean decorations and tank walls once a month but not at the same time as doing the vacuuming, usually 2 weeks after.  The tank has no heater and the temperature sits between 76 and 78.  I use Prime water conditioner but recently heard it may not be the best choice as it causes/can cause algae growth.  Not sure about that but maybe that's why I have brown algae?
I would appreciate anything you can tell about my nitrates and maybe suggest a better water conditioner if I'm not using what I should be.
Thank you.

Answer
Hi Carol:  I would change 10-20% of the water weekly and make sure you clean the gravel at least once per week maybe even once every ten days.  Prime is a good product to use but you can cut back on it or find a different product if you think it is the cause of the algae.  I would also take a sample of water to the local  fish store and ask them to check it for phosphate to see if that may be causing the nitrate and algae... let me know dave...