With sugar, you are putting some source of glucose or nutrients in the tank yes. but, with that word nutrients, I believe everyone uses it very lightly because of problems noone wants from those said nutrients, I understand but, high no3 can be a problem, and the fact maintenance is the only way to help, no3 can always be a problem for some.
Nitrates are "nutrients" to me. U get them because you don't have the nitrifying bacteria to keep them in check. You have the algae probs when no3 Is high because they are nutrients for algae.
Sugar is definitely not the answer for routine maintenance, because we don't have much knowledge of what it's actually doing BUT, I did it. It works. Sometimes newbe's need that help or restart if you will in the begining like me. I was doing wc and everything I was supposed to be (just like everyone thinks they're doing fine) however at the begining you don't have the Bioload experience or the tanks just to new to have the nitrifying bacteria to help.
I agree with increasing the nitrifying bacteria! But, that can take some time and your going to continue to go through he¡¡ with algae. And no3 will climb while your looking for some.
Long term, an increase of bacteria is what needs to happen! To help keep your tank where it's supposed to be. Go get some good live rock. I cycled mine myself separate from the dt to make sure I wasn't messing anything up! This way you can also save some money and get good dried rock to seed yourself with bacteria in a bottle or whatever.
Sugar- everyone knows no3 is super super small. That's why it can't be filtered out and wc is the only way to remove. (Idk specific dosing size, this is from my experience) Adding a half tsp of sugar like per 30 gal (I would do .5 tsp a day to slowly drop your no3) it's gunna take like 2 weeks, depending on tank size, to slowly drop no3. (You can cause shock to livestock if drop to fast) In that time you can be cycling rock somewhere and beating both probs at same time... No3 is able to consume glucose or whatever no3 likes in the sugar, thus making them bigger and able to be removed with the skimmer. You have to have a skimmer for this to work!
You will see a slight increase in your skimmers production as its skimming away no3. I knew it was doing this because no3 decreased. Skimmer increased. While no3 was decreasing algae probs were also decreasing. I say decreasing algae but it will not completely solve your prob. Deal with the GHA. get that rock cycled with bact, put it in your dt than get your clean up crew. All the crap algae your probably seeing now, nothing wants to eat it. But later with your no3 stable, you won't have crap algae so much hopefully and what will be there, cleaners should take care of. I would not add cleaners till u get new rock in there! This whole process could take a month.
Recap, look for some rock. I would definitely put in separate bin. If live, put in clean saltwater with power head and heater. Light if you have one. Wouldn't hurt. If you think it's good and full of bact, test it after a week for no3. If low put in your tank.
If dry dead rock, cycle in separate bin like I said but add bacteria to colonize. Your gunna want to cycle dead rock for like 4-6weeks with bacteria. Doing 50 wc after 2 weeks. No3 should show very low when ready.
Sugar- add .5 tsp each day to lower no3 in dt. Continue to test to make sure that amount is doing something and that your not dropping it to fast. Change dose amount need be.
(I would only resort to sugar if your no3 is higher than 30ppm if lower, just up your weekly wc)
Once your dt is low on no3, add rock when ready and get a clean up crew.
Then enjoy your tank! Just make sure to add livestock slowly giving nitrifying bact time to colonize and cover new fish.
Sorry for the book, I get excited