You're welcome! Yeah, it can go either way. I actually just seen a youtube video today for a planted tank set up and they were using the top fin one and liked it, that was why I mentioned it. The imagitarium is definitely my favorite, if you do go with it this is the heater I use, it's a little tricky because it is adjustable, but there's nothing telling you what you are adjusting it to, so it takes some time and error to get it set correctly, but it's been super reliable. Also, the imagitarium pump flow is adjustable and needs to be on the lowest setting for bettas or it will blow them around. It took me forever to figure that out lol. Good luck!! Post a picture when you decide on a tank and get it set up :)
Yep, I completely get that. The sponge filter and pump to run it would be >=15$ on Amazon (the links are from Amazon), and would be a huge improvement.
This looks like a pretty solid heater, and is adjustable which is far better than a preset one. Don't bother buying one in store; they're always crazy overpriced
Marina Submersible Heater for Aquarium, Mini, 25-watt https://www.amazon.com/dp/B00AFELT92/ref=cm_sw_r_cp_apa_gdINybA93N2VN
Also 15$
Don't depend on plants to filter your tank. It's very difficult to have enough plants to be able to use up all of the fish's waste, especially in such a small tank. It would also be very expensive to get the proper light, substrate, and fertilizer for a heavily planted tank light that
Java ferns are great for bettas, but make sure to keep the roots above the substrate. Mine loves sleeping both on the leaves and in the roots of his.
Ok, that does make me feel better. With that I think you can narrow down the issues to water quality (which you won't really be able to know until you get the liquid kit, since the strips don't have ammonia and aren't really accurate) or temperature. One of the issues with tanks so small is that there's so little volume that it's hard to regulate the temperature, especially when there's big swings in the room it's in. If upgrading to something that's more stable is out of the question, I would at least get an adjustable heater. I've got this one in my 2.5g shrimp tank and it works great.
Definitely stick with Aquaclear. As far as HOB (hang on back) filters go, they are the best. And you can't go wrong with more filtration. A good rule of thumb is to get a filter that is rated for double your tank size, so I would go with an Aquaclear 20 for that 10g. And an Aquaclear 30 should do perfectly fine on that 20g.
Assuming you do go with the Aquaclear, they have an adjustable flow so that you can set it to your liking and just position it so that it doesn't disturb your beta.
As for the heater, you'd want a 50 watt heater but it's usually better to get two smaller heaters than one large one so as to prevent disasters. In my 10g I have two of these.
50W seems a bit dangerous for a tank this size. Fluval has a model of their own that fits, according to Amazon reviewers, at both 50W and 25W powers. Might just get that. Small, from the same company, rated for every drop of water and no more in the Spec V, and cheap at $15.
These have always worked great for me:
Fluval Marina Submersible Heater for Aquarium, Mini https://www.amazon.com/dp/B00AFELT92/ref=cm_sw_r_cp_api_i_R1WQSWP45NYC6Q7V89GP
You should be fine with 25 watts for a 5 gallon.
I could never find an inline heater aside from the Hydor one, which looked iffy. You could look at the Marina, uh 15? Watt? Heater. Small profile and easy to hide, with adjustable thermostat.
Guess it's 25 Watts. Anyway, here https://www.amazon.com/Marina-Submersible-Heater-Aquarium-25-watt/dp/B00AFELT92/
So this one would be good for my set up? I will need to see if my tank is tall enough. Marina Submersible Heater for Aquarium, Mini, 25-watt https://www.amazon.com/dp/B00AFELT92/ref=cm_sw_r_cp_apa_qF21AbAKT0S6H
Anecdotal, but I have this 25w in my 5 gallon, set as high as it can go, and it barely keeps the water at 75 now that it's almost winter and the ambient room temp is lower. So yeah, I'd go with the 50w.
The cheap $2 glass thermometers work fine, imo.
I use this in my standard-size 2.5g. It's just baarely short enough to fit when the bottom tip's dug into the substrate. But your tank looks taller than mine.
I have 3 of these Marina adjustable 25w heaters, in tanks from 2.5 gal to 5 gal, and they are working fine.
I use this one.
They can survive without one but they won't breed at lower temperatures. If you want them to, this is the adjustable heater I use in my 2.5g and it works great.