Might be all wrong but

this is what i have.

20gallon
hob
live sand/rock(10lbs)
clown fish
engineer goby(LFS said was fine for a 20 gallon.I havnt had a chance to take him back because obviously he is not fine.He is about 4 inches)
power head
t5
heater
10 snails
5 hermits
emerald green crab

test kit says all is well.Everything is at 0 and the ph is good
phosphates are at 0

I do a 20% water change every week.Most of the time using RO water(sometimes not just because i live pretty far out and its not always easy to get to a LFS)

My sand is nasty and i have a green algea problem.What do i need to change?

 

The weeks you are not using the RO water are not helping IMO
tap water varies by location and on a week to week basis , so it really is the russian roulette of the reef tank world IMO

you seem to have GHA and cyno - thus there are nutrients available which may in part come from tap water and also from your feeding amount and types of foods

what flow have you got in terms of the power head , more flow can help prevent cyno getting a decent foothold (not 100% certain but can help)

what media do you have in the HOB filter? if your not running carbon and GFO at present , I would certainly suggest introducing those 2 into your set up

the algae you have needs to be harvested , whilst running the GFO which will then absorb the released phosphates ( manually removing whilst not running GFO is an uphill battle)

feeding - less dry foods , and frozen foods need to be thawed and the resulting liquid poured away before feeding your tank

the above should help

Steve

 

If its not easy to get to a local fish store than you really need to invest in a ro/di unit. They are crucial in any reef tank. Your water has so many things in it from metals, silicates, chlorine, etc. RO/DI takes all that crud out for you and unless you keep using the same water, well your gonna have the same water quality in your tank. You mentioned you have a HOB, are you running anything in it like carbon or more importantly something with GFO in it. That will help you in your fight. 20% wc should be putting a dent in it... but unless you keep using some other water that has some number of TDS in it your gonna have a algae problem.

Seriously do yourself a favor and get one they're not that expensive in comparison to all the money in gas, livestock both to help rid like a cuc and those you may lose during this outbreak, equipment to fight the algae, power heads to add flow ( still may be a good idea), water at the lfs, it adds up... Im SO glad i got one. I wish rodi units were mandatory in this hobby. like no tank is to be sold without one.

You may also want to beef up your cuc for now. give reefcleaners a look see. John rules hell hook you up for sure.

Good luck...

 

You say everything is at 0... What kind of tests are you using... also they more than likely are reading 0 because all that algae is using them up. In reality they are there, or else this wouldnt be happening.

 

Opinions on using prime for the tap water treatment.Also you can go to groccery store and get pure water by the gallon way better than tap.

 

If you chose this route than pick up a handheld TDS meter.... Point being is if anything other than 0 tds goes in your tank. more chances than not, your going to have a phosphate/nitrate problem.

If its 0 tds from the local grocery store, by all means do it. But this still requires gas , and the price now a days. your gonna spend the price of an rodi unit within a yr. so why not save the money and get one now and eliminate it.

Imo, if you truly see yourself doing this for the long term you need an rodi unit. Ask any successful reefers around here, your area, any where i bet they have an rodi unit in house, ready to go with remade rodi water and salt water mixed. this is so useful when you need some water at 10 at night and everywhere is closed.

just trying to make it clear how essential, especially in your case, an rodi would be in the long term success of your reef.

 

You've definitely got a nutrient problem. You are going to need to do a series of water changes over a period of time to get the stuff to go away.

I would:

- Buy an RO/DI unit. This will be the best $120ish you will spend in this hobby

- Do a 5 gallon water change using RO/DI water/salt once per week. As you do them, siphon out at much algae as you can. Do this until the algae is under control.

- Get some algae eating clean up critters in there.