Reddit reviews Python Pro Clean-Mini 1" x 6" Tube with 6 ft. Hose

Here's the gravel vacuum I use: https://www.amazon.com/gp/product/B0002APRT2/

It's got a nice low flow rate which is helpful for smaller tanks because otherwise you're done with the water change before you've actually had enough time to work through much gravel. I'd also recommend getting the squeeze-starter: https://www.amazon.com/gp/product/B0017JHPA6/

I actually never do that, I always think it just makes the fish stressed out. Here's my routine:

1. I use a mini siphon to take out 25% of the water
   
   
2. Dump out the bucket I put the dirty water in, and rinse it out, then put new, clean water in with some dechlorinator. I use Prime. I always just use my hand to feel that the water is close to the same temperature as what's already in my aquarium.
   
   
3. Very slowly pour the new, clean, dechlorinated water into the tank.
   
   
4. That's it! I always double check my filter to make sure it's not too gunked up, and clean that as necessary, but that's usually like once a month or less.
   

I use this one for my 5 gallon tank, it works well for me. I use a 5 gallon home depot bucket to drain in to.

https://www.amazon.com/Python-Pro-Clean-Mini-Tube-Hose/dp/B0002APRT2/ref=sr_1_2?crid=2MJBGM3XMWERL&keywords=python+mini+siphon&qid=1567359317&s=gateway&sprefix=python+mini%2Caps%2C175&sr=8-2

Personally I think it is algae, and your choice in gravel is probably contributing. It's a little on the large size, which means tons of crevices for the detritus to build up in that are difficult to clean properly. So even if you're doing regular water changes, unless you're also regularly and vigorously stirring up the gravel to raise all the junk into the water column, it all just sits. A plant would definitely help.

So two options. First fix is to switch out to a finer substrate. If you choose sand, it still needs maintenance because it can grow anaerobic bacteria and so will need to be gently agitated when you do water changes. A smaller size gravel wouldn't need it, but would still benefit from occasional shifting.

The second option is keep everything as is but be extremely aggressive with your cleaning. If you do that you'll need one of these so you can remove the fish from the tank and get the job done without stressing him or injuring him. What I mean by aggressive, is to remove the decorations, then use your hand or some sort of utensil to stir up the gravel. Specifically to put all the gunk into the water that you will be exchanging.

With the latter option there are two choices. For the first time, you can actually choose to strip the tank and fish the gravel out to deep clean into a bucket or tupperware or something. This is the method I'd choose because then the next water change will be much more clean since you're essentially starting with newer cleaner gravel. Do not wash the gravel with tap water, use the tank water. There's beneficial bacteria in the gravel by now that die from chlorine(tap water)

Choice number two is the lazy way, you just stir up the gravel and do several water changes over a week, but during that time your tank will still look dirty because of all the mulm and algae in the water. Also there's a good chance that the algae will get worse first before better as it's eating the nutrients.

In the end though I think these ways are how you'll get the best water for your fish and fix this issue. I wouldn't use any algae killers, since that's not actually solving the root issue here. I would strongly suggest you also get a plant but only after your water has become more clear because that way it has a chance to establish itself and not get choked out by the algae.

As a side note I don't know how you're siphoning your water out, and if you don't have a gravel vac might want to consider getting one.

It sounds like you may be feeding too much if that much food is uneaten and sinking into the gravel. Can you provide more info on your setup and feeding routines?

Here's a great video that shows you proper gravel vacuuming technique including how to start the siphon and how to control the water flow to separate the debris from the gravel (crimping the line).
https://www.youtube.com/watch?v=LYv5n0a85OY

This is the gravel vac that I use on my 5 gallon tank. Get the size rated for your aquarium.
https://www.amazon.com/Python-Pro-Clean-Mini-Tube-Hose/dp/B0002APRT2

I've got:
Python Pro Clean-Mini

As well as the squeeze starter reccomended with it and it works well. I use it for cleaning and water changes (as they go hand in hand).