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Kniquy, I think personally that when you disturb the top surface of an old sandbed you reveal a new quantity of nutrients, that was buried and to a degree locked in by the original surface of the sand (old sand bed surface layers tend to be a bit clumped from some organic type glue I often find). So every time you scoop a bit more out, you release more to the tank. 8 years is pretty old too and I'm not sure how many people manage to keep a sand bed going that long (I'm now BB so all this is behind me but speaking from several years experience with sand beds). Especially if its not deep (deep, like 6 inch, sand beds last longer IMO. A 2 inch 8 year old sand bed is almost bound to have problems IMO).
If it were me and I wanted to keep the sand bed, I would take stock out and put in a bucket of clean water siphoned from the tank before disturbing anything (so its as clean as point of sale), then remove / siphon the sand bed entirely. If you want to keep the water, siphon the water out before disturbing the sand. Then either get new sand, or if you want to reuse the old stuff, although I think its quite hard to clean, you can have a go. Get some tough rubber gloves because this destroys your knuckles - put the sand in a big container and run water through (while outdoors) so its overflowing, and spend a few hours stirring the sand vigorously with your hand. This washes the sand of solid debris. Then, although I have never done this, if I was to clean sand nowadays, I would use an acid bath, probably using clean hydrochloric acid, like a gallon of muratic acid (about 30% strength) in 10 gallons of water. If the sand is really fine this might not work but for the coarse (1 to 2 mm) sand I used to use I think this would work. Keep stirring with your gloved hand for a couple of minutes every 10 mins, for a couple of hours maybe. Or maybe use stronger acid for shorter time. Hydrochloric acid will strip the outer layer of sand so it should look bright and clean after, and it will strip the bound phosphate from the sand grain surface. Then rinse for a couple of hours as above, overflowing the water and stirring, and it should be OK to go back in the tank then. Before putting live stock back in tank it would be wise to check pH and alk to make sure the acid is completely washed away.
I used a paint stirrer which I stripped of paint before using it in the past to violently stir sand, so the abrasive action of sand grains against each other would scrape the outer surface while rinsing.
Or, just buy new sand. You got yo rmoneys worth if it lasted 8 years!
Also clean the crap off the pump and rocks if possible. I've done this with a soft brush in the past, it dosent destroy life on the rocks but removes the fragile gunk algae. Do this in salt water though (like the old tank water) so it dosent kill the rock bacteria and little critters on the rock.
Then with all that nutrient rich stuff removed, you will have a chance IMO. But with the sand bed as it is, probably full of nutrients and carbon sources, I think it will be hard to get on top of.