Mr. Saltwater Tank TV Friday AM Quick Tip: Don’t Miss A Spot Ever Again

Algae on your tank’s glass can be removed with an algae scraper. Yet you always get those pesky spots that have to be scraped off by hand. The hard part is making sure actually scrape the algae off when you can’t see where you are scraping.


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Comments for this article (20)

  • Melanie Simpson says:

    Hi Mark,

    For hand scraping algae I use an old credit card. It seems to work well also. And who doesn’t have one of those laying around. Melanie

  • Carlos says:

    A white exfoliating glove on your hand removes the film while providing a background to easily see the hard spots. Remove them with a credit card. No going back and forth from side to front, no cleaning grease pencil off the outside glass, no collection of dangerous rusty razor blades. Gloves are cheap on line or in any bath shop, usually a few per package, use the extras to smooth your skin.

  • Thea says:

    Instead of a grease pen I use a post it note. You can keep reusing it for a long time before it becomes un sticky.

  • Daniel Gappa says:

    Grease pen sheesh… Just lick your finger…

  • Greg Duffy says:

    Melanie Simpson,

    Do you really want to put a credit card into your tank? Who knows what kind of chemicals are on that card? Even if you wash it, there could still be chemicals, such as the glue used to keep the cards together seeping out or bits of broken plastic.

    The other thing to add to Mark’s advice is to not use that razor blade too many times, because razor blades rust very quickly, especially coated with salt water

  • Carlos says:

    Seriously?? Hobbyists have been using credit cards to clean glass forever, no one has ever reported one breaking off bits of plastic or oozing glue.

  • Greg says:


    Hey man, I just offered my opinion, no offense intended. Maybe I just be a little over cautious, but I don’t put anything in my tank that is not made to be in my tank! I’ve never heard about anyone using credit cards, but if anyone wants to use it any they have not experienced any issues, good for them.

  • Barbara says:

    Great Tip mark! That happens to me all the time.

  • Melanie says:

    Greg, I’ve been using a credit card for awhile now with no ill effects. Easy, works well and doesn’t rust. 🙂

  • Tom says:

    Mark, any tips on how to get those hairline scratches out of my glass that was caused from my algae scraper having a minute piece of sand in it?

  • Curt says:

    Hey Greg,
    I’m not trying to kick a dead horse or anything but rust is not a big deal in reef tanks either. What do you think GFO is?

  • noal Green says:

    Mark, I am reading your guide to nuisance algae outbreaks and am about to start dosing Dr. Tim’s Waste away. I have been running a Korallin bio-denitrator since the start-up of my tank and have never had a nitrate problem. My question is should I continue to run the bio-denitrator while fighting my algae problem?

  • Greg says:

    Ok, before this turns into a beat down of me, lol, I just felt like adding my .$02 in the matter. As I said before, I guess I am being over cautious. As they say, if it works for you, then go for it.

  • polojeff2003 says:

    I am interested in using a credit card. Do you cut in half, long ways to fit it in a razor holder on your magnet scraper? Hold it in your hand to use it? I want to try it.

  • Brandon says:

    im a big follower and im pretty sure this is a rerun
    its the same video as the one you put up 3 years ago lol

  • Melanie says:


    I just hold the credit card in my hand to use it. No need to cut in half, use as is. Very simple, works great!

  • John Yankanich says:

    Greg Duffy, it was one of the Friday morning quick tips to use a credit card or gift card to scrape the glass, or acrylic (because you can’t use a razor blade on acrylic). It works well, and if you just wash it off in RO/DI water it’ll be fine. It’s not like it’s constantly sitting in your tank and leaching all of the chemicals into it. It’s only in the tank for a short time period.

  • Integral9 says:

    Mr Clean Magic Eraser. Hooray for melamine foam. Probably not a good idea for acrylic though. I haven’t tried it though.

    btw. Careful using those razor blades. Depending on shape of the blade it could easily scratch the glass. My tank is living proof. Ideally, get the ones w/ the rounded corners to help prevent such atrocities.

  • Ruth says:

    Mr clean magic erasers work great on glass or acrylic. We use them all the time on customers tanks with great results. Just make sure you get the original (no chemica) version. Not the one with detergent in them. YIKES!

  • Pierre says:

    I won’t use any metal to clean the inside of a glass tank. Reason being that glass being rated about 6-7 and metal being close to 10 on the hardness scale its too risky.
    A friends wife did her hubby a favour and cleaned his torn down tank with steel wool outside on the lawn. Thinking she’d saved time she took him out back to show him her work, problem was the afternoon sun reflected on an angle about ten thousand scratches. when I tried to explain the material hardness scale she scoffed at it like I was a smart ass. Needless to say my friend bought a new bigger tank.
    I use a piece of Perspex or acrylic sheet as a scrapper which works a treat. the edge will wear down after a while, no problem I re-cut it to a sharp edge & go again.

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